I can also confirm that pretty much anything on the Source Engine (that isn't a mod) and Saints Row the Third also require Steam. So does Magicka. And Nexuiz. I think Lead and Gold does too. So does Hero Academy.

Going back, I think almost everything Paradox is DRM-free, meaning Victoria I & II, Crusader Kings I & II, Sword of the Stars (don't know about 2, 2 might need Steam), Europa Universalis I, II, and III, Hearts of Iron III...

At the very least, Gamersgate lists them all as DRM-free, and the Amazon versions just have a serial code activation. The Steam versions don't even have that, and Crusader Kings 2 is definitely DRM free, so I'd assume the earlier ones are, as well.

EDIT: Oh, the Dream Machine is DRM-free.

EDIT2: Dangerous Waters appears to be DRM-free, despite executables being named to the contrary.

Botanicula - just moved it to a new folder and deactivated the Steam client. Works fine as far as I can tell, despite having Steam Cloud support (yes, I also tried saving and loading).

Supposedly it also works for Assassin's Creed 1. A friend of mine tried it because her good PC is not connected to the internet. She claims that she simply moved the folder to her other PC and it worked right away. Kinda hilarious considering all the problems with the early cracks which would render the game unplayable when entering Jerusalem.

Amok says AssCreed uses CEG. I'm making a note to test it myself later.

Thanks for Botanicula.

when you said AssCreed I thought you meant this

http://i37.fastpic.ru/big/2012/0424/48/e03c76598286c797fa1a77057970f348.jpg

Confirmed:
Cogs


These requires steam to run:
Bully
Delve deeper
Depths of Peril
Future Wars
Gothic

I tried both again, could not get either to run without launching steam.

edit:
Delve Deeper behaves very strange when forced to run without steam, not sure if this is only on my system or not. Basically it runs when dismissing the error message, but it starts in some kind of test/debug mode which is unplayable.

Droplitz seems to also work without Steam. Thing is, I can't really test it because in both cases only a black screen shows up on startup but in both cases the music plays (and I don't know how to apply the "black screen fix" to the non-Steam version). Someone else should take a look at it.

Btw, my "do have DRM" confirmations:
And Yet It Moves
Aquaria
Blue Berry Garden
Braid
Crazy Taxi
Crysis
Chains
Obulis
Penumbra: Overture
Rip Trilogy

Sorry for double post, just want to make sure it's seen by OP:
Grand Theft Auto 2 definitely works.
Grand Theft Auto 1 probably works (even the legit Steam version crashes currently but with or without Steam - I do get into the main menu - so not DRM related it seems)

Grand Theft Auto corrupts its own save file on exit; you need to run the GTA fixer after each gaming session. This is not Steam related at all; I just tested it and it runs fine without Steam.

Ain't most Desura games DRM-Free

Confirmed:
NyxQuest: Kindred Spirit
Trauma


Requires Steam to run:
Babo - Invasion (do not run, behaves strange and stays active process)
Deus Ex GOTY
Grotesque tactics
Gyromancer
Infernal
The Maw
Max and the magic marker
Oddworld: Abes Exoddus
Oddworld: Abes Oddysee
Puzzle Agent
Recettear
Toki Tori
The Void
World of Goo
Yosumin

Seriously DRM free?! The non-Hd version on Steam required the client, so if this doesn't that's quite a surprise.

I tested it again now, runs without Steam client. Probably because of the new launcher (and someone forgetting coding in the DRM thing again...)

Nah, it must have managed to start an offline mode Steam without me noticing when I tried this yesterday and thought I had it DRM-free, because now there's nothing I can do to get it to start without calling the Steam client. It seems it's DRM after all :(

Man, I've had to correct myself on every post I've made in this topic today.... I must be losing my mind.

I better download it before they 'fix' it then. :P Thanks, part of the reason I hadn't played it much was because of it needing Steam client to run all the time on the non HD version

EDIT: Btw, Hacker Evolution Duality and Faerie Solitaire are DRM-free too

EDIT2: And Munch's Oddysee