Best secret spying methods

[Aleolus]

OK, I have a villain that will be coming up in my game before too much longer. He knows about the party and that they are a potential threat, but isn't wanting to take overt action against them quite yet. I am wondering what the most effective ways for him to keep an eye on them would be, while not giving the party any signs of it other than maybe a vague feeling of being watched. He is a Cleric 10/Aristocrat 4 who worships Vecna.

Also, as a side note, are there any PrC in published materials that are good at rooting out secrets and hidden evils through the use of stealth?

[Palanan]

If he can get within a few miles of the party, Chain of Eyes is a third-level cleric spell that allows you to see through the eyes of a creature you touch.

Better yet, you can switch to another creature the first one touches, and another and another. It's great for infiltrating human settlements where people jostle each other, and can be useful for creatures like birds in flocks, or friendly dogs, etc. At your cleric's level he should get 10 hours of viewing time per day.

You can't control the creatures whose sight you're using, so it's not quite your personal drone--but if you wanted to have eyes on the defenses of a walled town, you can cast the spell on a cart-horse heading inside the gates, transfer to the stable-boy, and on and on until you have a good sense of your target area.

[Feldar]

The villain is probably an upstanding member of the community, with some wealth at his disposal. Perhaps he is a reasonably wealthy but kind merchant who employs lots of people. If that doesn't fit, perhaps he works as a clerk for such a person. All of those things give him a network of eyes and ears, many of whom are truly innocent but who don't mind sharing "news" with each other or when their boss/co-worker buys them a round a the pub.

The villain is of sufficent level to have access to enchantment magics, certainly including divination-type magics (clairaudience and clairvoyance, divination, etc). What he can't gain from informants he can gain directly with divinations. He possibly has access to domination effects, which used judiciously and with subtlety and wisdom ("I am going to free your mind now. Once I have done so, you will have no memory of being under my control") can be used pretty freely against your average person with minimal risk of detection.

[Doctor Despair]

With the bind-vestige feat, improved binding, and practiced binder, you can get Malphas's ability:

At will, you can summon a dove or a raven to aid your powers of observation. (Use the statistics for a raven regardless of the creature’s form.) The bird appears perched on your shoulder. You have complete control over its actions, and you can see what it sees and hear what it hears. Use the bird’s skill checks to determine the results of its actions and observations (for example, Bluff, Search, Spot, Listen), but use your skill bonuses to derive information from its observations (for example, Knowledge, Sense Motive, or Spellcraft to identify a spell). If you have the trapfinding ability, you can use the bird to fi nd traps so long as doing so doesn’t require it to manipulate an object. The bird cannot talk. You can have only one bird summoned at a time. It remains until you summon another dove or raven, mentally dismiss it (a standard action), or stop binding with Malphas.

You can also use the feat Mother Cyst to use Necrotic Cyst on local vermin and animals, then use Necrotic Scrying to spy on the party.

Both of these seem fairly thematic for a villain.

[Batcathat]

It might be a good idea for the villain to use both magical methods and mundane ones, like sending spies or people to infiltrate the party somehow. If he's lucky, the party might only prepare for either magic or mundane. Plus, if they discover one way he's keeping tabs on them, they might feel safe and relax (though obviously that's not a great tactic if he wants to stay completely under the radar. Except maybe if he can frame someone else for the spying?)

[Aleolus]

The villain is probably an upstanding member of the community, with some wealth at his disposal. Perhaps he is a reasonably wealthy but kind merchant who employs lots of people. If that doesn't fit, perhaps he works as a clerk for such a person. All of those things give him a network of eyes and ears, many of whom are truly innocent but who don't mind sharing "news" with each other or when their boss/co-worker buys them a round a the pub.

The villain is of sufficent level to have access to enchantment magics, certainly including divination-type magics (clairaudience and clairvoyance, divination, etc). What he can't gain from informants he can gain directly with divinations. He possibly has access to domination effects, which used judiciously and with subtlety and wisdom ("I am going to free your mind now. Once I have done so, you will have no memory of being under my control") can be used pretty freely against your average person with minimal risk of detection.

He is actually one of the lords on the city council (no one knows he is a cleric of Vecna, obviously)

[Feldar]

There you go. Not only does he have ears, he probably has toadies eager to gain his favor as well, merchants and others willing to share information as well as gold in exchange for remaining in his good graces. He has a network of networks. He doesn't bother gathering information himself except when needed, instead devoting himself to his charitable works serving his community as insurance against the day when he needs to flee and will want the townsfolk to assist him against the "evil people" trying to frame/kill him.

[Aleolus]

I suppose that would be easier than the idea I had bouncing around, of having an Invisible Stalker start following them around.

[Doctor Despair]

I suppose that would be easier than the idea I had bouncing around, of having an Invisible Stalker start following them around.

A level 1 Binder with Improved Binding can get invisibility at will from Malphas ;) And they could use the dove-spy, too

[Aleolus]

Ah, but with Malphas' invisibility you are subject to Invisibility Purge, and a See Invisibility spell would let them see you, whereas with an Invisible Stalker, Invisibility Purge does nothing, and See Invisibility just shows 'a dim outline of a cloud.' Only True Seeing really reveals an Invisible Stalker.

[Palanan]

Is your cleric of Vecna in the same town as the PCs, or some distance away?

And what level is the party?

[Aleolus]

Same town, and if I remember right my PCs are all level 8 equivalent. It's been a while since we met, and they are all playing races from Bastards and Bloodlines which either were given a +2 LA or I felt the LA listed was too high and lowered to a 2. A Piper, a Watcher, and a Houri (as well as a dwarf NPC I added to give them a bit more melee ability)

EDIT: Though I should mention that the group will most likely be leaving the current city for the time being by delivering a letter to someone in the city I have been making and waiting for a reply (this is mostly a way to let them see what I've done in the city so far, but I think I am incorporating it pretty well)

[Calthropstu]

Simple. Hire the party to escort him and a hastily built caravan to the middle of nowhere where a "terrible plague has struck. We need to deliver these medicines right away!" It's dangerous in the wilderness, and passing it off as a legit job, when the caravsn gets attacked, not only will he get a sense of the team's combat capabilities, he'll get to sniff out their personalities and likelihood that they will interfere with him. Treat it as a legit job the entire way through, pay the party, and build up a strategy to defeat them.