Okay, I've updated the list with all the new comments here. Thanks again, guys! I also added Sonic Adventure DX, which needs Steam.exe to be renamed in order for it to not start the client.
(full disclosure: I'm one of the developer and I'm outrageously posting it here) BOMB
is the aerial-combat game you get when you mix Crimson Skies and Porco Rosso.
No DRM whatsoever, you can copy the game's folder and put it right away on your USB stick or BitTorrent!
One limitation though: no server browser outside of Steam, just direct IP connections.
edit: sorry, can't post URLs at the moment
Holy crap, I love people like you. I need to buy your game just to support you guys for being so cool! Is it both the Windows and Linux versions that are DRM-free? Thanks again for the info!