Although most deities live on the outer planes, a few live on or are closely related to the plane of shadow.

God of Fools, the Hidden One, Trickster of Tricksters
Demigod (Neutral Evil)

Dolus is a god of trickery, but he displays his trickery in a quite unusual way. Instead of inspiring his worshippers to trick others, he tricks his worshippers. He cares not who or what his thralls think they are worshipping, as long as the power of that worship goes out to him. Due to his nasty habit of stealing worship from other deities, he fears retribution too much to live on the outer planes. Instead, he lives on the Plane of Shadow, where his angry brethren are unlikely to ever find him. Dolus’ holy symbol, or its closest equivalent, is a featureless, black circle. All formal worshippers tattoo this symbol somewhere on their body.
Anyone is a potential worshipper of Dolus, even if they do not know it. Dolus commonly floods the plane of shadow with his divine essence, increasing the odds that cultists (see earlier post) will call upon him instead of their desired source of power. There are a very few individuals who know Dolus’ identity, and have, as an act of worship, set out on a quest to meet the hidden one himself. Dolus’ views towards his direct worshippers, as of yet, remains to be seen.
Although Dolus actively teaches nothing on his own behalf, his few direct followers have learned from example and gain power, complete tasks, and manipulate others without doing so much as revealing their faces.
Portfolio: Secrecy, Manipulation, Shadow
Domains: Technically, Dolus grants access to every domain. His few direct worshippers, however, are limited to the Secrecy, Shadow, Evil, and Trickery domains.
Cleric Training: The only training that a cleric of Dolus truly needs is the discovery of Dolus’ name and identity. This task has not been made easy, however, and may require several divination attempts, an interrogation of another cleric of Dolus, or the recovery of ancient lore depicting him.
Quests: Dolus doles out no quests. Instead, he allows his followers to assign themselves tasks. Clerics of Dolus make it their mission to meet Dolus, face-to-face.
Prayers: Dolus accepts all forms of prayer with equal glee. As such, his few actual clerics usually choose to keep their prayers simple and quiet, knowing he will not mind.
Temples: Dolus has many temples, spread out amongst the planes. Actual temples dedicated to him in particular, however, are nonexistent. A cleric of Dolus can send their worship to their deity from anywhere and a shrine of Pelor would work just as well as a shrine of Wee Jas.
Rites: Despite the lack of formal rites, it is customary that if someone sees the face of a cleric of Dolus against their whims, that they mutilate, or magically alter their face.
Herald and Allies: Dolus’ one ally and friend is his herald, a Gloom (ELH, page 192).

Mae Kiar:
Reclaimer, Watcher of Darkness
Lesser Deity (Neutral)

Mae Kiar is a deity of, for lack of better terms, justifiable vengeance. Formerly an abyssym, she slew the balor that owned her family’s souls and took his soul in turn. This remarkable act of vengeance allowed her to ascend. Mae Kiar watches for dark acts and sends her worshippers to claim vengeance for those unwilling or unable to claim it themselves. Seeking nothing from her divine kin, she has isolated herself on the plane of shadows, where she claims evils can be seen earliest. Although she is dark with her verdicts, she is not nearly as cruel as Cas (deity of spite, see heroes of horror for details). She appears as a humanoid woman of indistinguishable race, surrounding by a blurring shroud of shadow and possessing two piercing red eyes. Her holy symbol is a fist, with a long crack running down its center.
Mae Kiar’s cause appeals to few out there, but some individuals see her teachings as appealing, and so worship her. She is a bit contrary in that she attracts and supports both evil and good worshippers. Evil worshippers look to her as a deity of violence, torturing and slaughtering portrayers of other dark acts with utmost glee. Good worshippers look to her as a deity of protection, protecting the downtrodden against those they cannot fight against on their own. A few warlocks look to her as a paragon, one who was able to escape her curse.
Portfolio: Vengeance, Justice, Shadow
Domains: Evil, Good, Shadow, Wrath
Cleric Training: Clerical training of Mae Kiar involves personal training by an elder cleric, culminating with a mission from the church.
Quests: Mae Kiar’s missions always involve the righting of a wrong or the punishment of a wrongdoer. She is careful to give missions only to followers with an appropriate alignment for that mission.
Prayers: Prayers to Mae Kiar always a proclamation of evils bested and those yet to be destroyed.
Temples: Shrines to Mae Kiar are surprisingly common, appearing in good and evil towns alike, as well as on lesser-known roads. They are often small and hidden in shadow, however.
Rites: The most famous of Mae Kiar’s rites is known as “the acknowledgement”, listing the name of the last evil thwarted before destroying a new one.
Herald and Allies: Mae Kiar’s Herald is a unique dark trumpet archon of neutral alignment. Her planar allies include concordant killers (see MM IV) and, surprisingly, the rilmani (see Fiend Folio).

Moon Maiden, The Silver Mistress
Greater Deity (Neutral Good)

Deity of the moon and tide (and on occasion, love), Mutart is one of the older deities in the current pantheon. She appears as a human or elven (the exact race seems to change over time) female, wearing a long, silver dress. Her skin and hair looks pale and silvery as well, but she possesses glowing blue eyes. She seeks relatively little from her worshippers, impacting their life directly as little as possible. Her holy symbol is, in most cases, a crescent moon, although full moons are sometimes used as well.
The Moon Maiden, more often than not, appeals to sailors, who often need the moon’s light or fear a rough tide. Poets, writers, and other romantics also pay her homage from time to time. Most who worship her, however, are lycanthropes, who she feels particularly responsible for and who are the only ones to possess full moon holy symbols. Some overzealous religions relate presence of her churches (perhaps rightly so) to lycanthrope attacks, and so seek to drive them out.
Mutart teaches that just as the sun illuminates, so does the moon as its reflection, a fundamental lesson taught to most shadow magic users as an example of reflection. By the same ticket, this lesson has inspired many diviners to work in unusual ways. She also teaches that the moon calls out, to lovers, to the tide, and, unfortunately, to lycanthropes.
Portfolio: Moon, Love, Ocean, Lycanthropes
Domains: Good, Moon, Ocean, Oracle
Cleric Training: Clerical training of Mutart is individualistic. As soon as an individual considers themselves worthy to be called a cleric, Mutart will accept them as one.
Quests: Mutart’s missions are few and far between. She allows clerics to decide how they should proceed, for the most part, so long as their goals to not contradict her own..
Prayers: Mutart’s prayers differ from area to area. In one country, prayers to her may be complex hymns. In another, they may be poetic recitations.
Temples: Mutart’s temples are grand and tend to be poetically placed, such as on the top of a large hill or on a seaside cliff.
Rites: It is customary among clerics of Mutart to bow ones head whenever one sees the reflection of the moon upon water.
Herald and Allies: Mutart has no true herald, instead claiming each moon acts in its own way as her herald, which she can make appear larger, smaller, or change color to signify events to entire worlds. Her planar allies are celestial or half-celestial lycanthropes.

Lord of Madness, Father of Croob
Lesser Deity (Chaotic Neutral)

Teka is a deity that stands for nothing. His deific power was a terrible mistake that drove him to insanity. He appears as a floating, black brain, covered in cracks, as if about to shatter. Teka does not, and indeed cannot, leave the Plane of Shadow. His holy symbol is a black and cracked skull.
Since Teka’s ascension, he has formed the croob in a fit of madness, and through them, the galks and geluks. These individuals are among Teka’s only worshippers. A few small cults on the material plane worship Teka as well, but the number of individuals in these cults is far outweighed by the hordes of Teka’s creations. Teka’s enemies include most sane deities and individuals, although they are content knowing that Teka’s mind is no longer capable of forming a proper long-term plan.
Though Teka teaches nothing, the Geluks have made it their business to interpret every garbled message of Teka into a tangible message. The entire mass of “Tekan” philosophy encompasses several material plane philosophies.
Portfolio: Insanity, Mind, Shadow
Domains: Chaos, Madness, Mind, Shadow
Cleric Training: Clerical training of Teka is best left undescribed, consisting of several atrocities, the least of which is self mutilation of the brain.
Quests: Teka’s missions, even as interpreted by the Geluks, seem to make little sense. Some missions call for massacres among the croobs, while others call for peace treaties with buffalos. If the Geluks are trying to turn Teka’s thoughts into a plan, it is impossible to see where it is going.
Prayers: Prayers to Teka consist of screams, moans, and gurgling noises. As such, one listening to a church of Teka may come to assume it is a torture chamber.
Temples: Shrines to Teka are made ridiculously big, at the orders of the Geluks. Sometimes, the croob have to squeeze their way around a church to get to their home each day.
Rites: Teka, according to the Geluks, accepts several rites, each of which is worse than the atrocities of clerical training.
Herald and Allies: Teka, lacking the sanity to gather forces, has neither herald nor planar allies (unless the croobs, galks, and geluks are to be included in such a category).

Honorable Mention
Although I can not give its statistics and have only just remembered it, I feel that an honorable mention should go to the Shadow, member of the Dark Six from Ebberon. For purposes of Thoroughness, I also mention another deity of shadows, Erebus, from Dragon issue #322 (which, interestingly enough, is the first source to mention the Nightshade Covenant and creates the basis for shadow elementals as Darkness Pseudo-Elementals. I’d advise you to get the issue: it’s a great shadow magic history lesson, If you know where to look).