PF - Best Infiltrator or Recon Creature in PF?

[unseenmage]

What creatures make the best unseen information gatherers? Players and DMs alike could benefit from a list like this both so each know what creatures they can employ and so they know what creatures they might need to defend against.
If there are enough responses I plan to split the list up into categories: Infiltration, Reconnaissance, Surveillance, etc.

Creatures viable for this thread are those who can spy effectively. Gathering information, doing so unseen, and getting past barriers would seem to be the most important abilities. With each creature you list please try to include either a link or a source with page number.

Also, try to add one sentence with your submission detailing why it is good at what its good at. This could be as simple as a list of ability names like Invisibility that are self explanatory.
Thanks for reading and thanks for (hopefully) contributing! Lets list us some spies.

Clockwork Spy (http://www.d20pfsrd.com/bestiary/monster-listings/constructs/clockwork/clockwork-spy) (Record Audio)
Mnemor Devil (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Mnemor) (Easily Forgotten, Memory Siphon)
Quasit (http://www.d20pfsrd.com/bestiary/monster-listings/outsiders/demon/quasit) (invisibility, change shape)
Thought Harvester (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Thought%20Harvester%2 0Robot) (Harvest Thoughts)

[avr]

Accuser Devil (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Accuser%20Devil%20(Ze bub))(invisibility, greater teleport, records & passes on memories)
Raktavarna Rakshasa (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Raktavarna) (change shape into item, remote reporting via master's eyes)
Dandasuka Rakshasa (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Dandasuka) (alter self, detect thoughts, clairvoyance)
Janni Genie (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Janni) (invisibility, ethereal jaunt, plane shift, not evil)
Umbral Shepherd (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Umbral%20Shepherd) (possession!)

All of the above can be accessed via lesser planar binding, albeit you may have to go to another plane first to catch the outsiders native to the Material Plane. To get creatures with nondetection (as detect magic will catch many of these tactics) you'd need to scale up to bigger creatures via the normal planar binding, or provide it yourself or otherwise.

A special note here for svirfneblin who have some of the racial abilities most suited to spying you'll see - including constant nondetection.

[Arutema]

Observer Robot (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Observer%20Robot) - Stores more audio than the clockwork spy and has camouflage. Can also transmit video back to you if you have suitable tech to receive the stream.

[Necromancy]

Gnome alch at high levels

[Florian]

Once you pick up the Summon Guardian Spirit feat, you can access the Guardian Spirit template and anything goes, especially if based on a critter that has already been named here.
(The summoned monster gains personality and retains memory. Even if your scout is lost, you can re-summon it to gain its knowledge)

[meschlum]

Anything with enough hit dice to become a Nightmare Lord. Besides Invisibility, slow flight, and phasing out of reality, you get permanent Dominate Monster via dreams. So the castle you want to spy on soon has every servant obeying your instructions, and then you take over the more important figures too.

[Sayt]

Invisibile stalker? Can walk/float through invisibility purge traps.