While in the subject of
The Pandorica Opens, my Omega theory isn't holding up too well, especially after watching
The Lodger myself, and finding out that the unseen alien threat was pretty much explained as artificial mechanical intelligence doing horrible things for simple program reasons (ala the Clockwork Droids). But on the bright side the number of returning monsters and aliens are not just plain ridiculous, complete with several races that at the very least will be mentioned but unseen.
Here's a list of whose concerned:
Daleks (new model / pure bloods)
Cybermen (Cybus version, though rumors mention original versions as well)
Judoon (one at least)
Sontarans (Christopher Ryan returns, but playing a different character from General Staal)
Sycorax (trio of which)
The Slitheen (at least mentioned by River Song)
The Terileptils (originally from
The Visitation, at least mentioned by River Song)
The Nestene Consciousness (at least mentioned by River Song, though newspapers say the Auton costumes are present)
The Drahvins (the all-female fascist from
Galaxy 4, at least mentioned by River Song)
The Chelonians (cybernetic killer tortoises from various spin-off novels, at least mentioned by River Song)
The Atraxi (giant flying eyeballs from
The Eleventh Hour, though among the few here that are unconfirmed)
The Zygons (from
Terror of the Zygons, and are too unconfirmed)
The Draconians (from
Frontier In Space, at least mentioned by River Song)
Silurians (the female warriors introduced in
The Hungry Earth and
Cold Blood)
The Pilot Fish (better known as the Robot Santa Mercenaries from
The Christmas Invasion and
The Runaway Bride)
Weevils (from
Torchwood, and there are at least two standing alongside the Silurians in photos)
Blowfish (recurring fish-headed alien criminals from
Torchwood)
Hoix (brutal monster / alien from
Love and Monsters as well as the
Torchwood episode
Exit Wounds)
Uvodni (bug like aliens of whom the anti-hero General Kudlak is a member of, from
The Sarah Jane Adventures)
Bracewell (not a villain by any means, but the lovable android with human emotions from
Victory of the Daleks, and is one of many good guy characters to at least make a cameo in the final two episodes of the season, along with Winston Churchill, Liz 10, Vincent van Gogh, Amy Pond as a child, and what appears to be a Roman soldier who looks a lot like Rory

)
Plus it seems that the Yeti will be making a comeback in the 2010 Christmas special, according to some new concepts art that has popped online:
http://www.darkhorizons.com/news/17513/ ... doctor-who