You might like these then:

Another Space Hulk PC game (and I believe it has a level creator/editor)
http://r.vinot.free.fr/spacehulk/index.html

Space Hulk SP 1.0.9 (if you can find it that is as the project died and the files removed from the SourceForge page, but it was a working version which I quite enjoyed playing. I think it's levels were the same as those in the original Space Hulk campaigns, too.

Actually, there are some mods of Alien Assault that convert it to a Space Hulk game. It was originally out as a Space Hulk title, but Games Workshop sent out a 'Cease and desist or we sue your asses out of existence' order, so they had to change it to Alien Assault.

i think that no one has talked about the amazing Spelunky!

http://www.spelunkyworld.com/

quite good and nicely freeware! ^__^

Company of Heroes Online (Open Beta): http://www.companyofheroes.com/
Age of Empires Online (Open Beta?): http://www.ageofempiresonline.com/downloads/
Lord of the Rings Online (free-to-play): http://www.lotro.com/

--additional comment--
I don't know about AoE but CoHO is supposed to be free2play when it comes out.
Also, minecraft!

some casual game http://www.gametop.com/

FPS Trainer

http://www.fpstrainer.com/

Ministry of War is without any doubt, the BEST browser-based RTS ever made (So far). You can level up heroes and arm them with weapons and armor and skills, the combat is REAL TIME, and it has many innovative features such as religious dominance, endgame content, lairs that can be attacked (Raids if you will), zone wars (Take over other areas if I'm not mistaken), city sieges (Literally), and trace Seriously, I can't stop playing. Enjoy.

"Planescape Trilogy", three modules for Neverwinter Nights 2. Still in development.

http://www.roguedao.com/

Warlock's Gauntlet

Holy shit! DOWNLOADING!

Stargunner, by 3D Realms:

free full game: http://www.fileshack.com/file.x?fid=7247

free soundtrack: http://www.fileshack.com/file.x?fid=4379

I know someone already listed UFO: Alien Invasion a year ago or so, but there was a new release last month that everyone is saying makes it waaaay better in every way. Just be sure to search the forums for the +city map bug patch before playing, apparently someone made a little mistake on one of the level rebuilds; I'm certain it will be fixed in the next update.

To anyone that isn't familiar, UFO: Alien Invasion is a freeware, open-source XCOM: UFO Defense style game. It is basically a more modern version of XCOM with a totally new story, graphics, aliens, etc. The graphics and sound aren't the best but they're serviceable, and it's definitely a work in progress. Regardless, it's the closest you'll come to XCOM without replaying the original (after 15 years there's just no more surprise in the alien autopsies, sigh).

It runs on a heavily modified Quake II engine so the system requirements are pretty low. It takes some getting used to but after an hour or so of effort I was totally into it.

Ruiner, an already good looking third person hack and slash mod, for Doom 3. There's a demo out with 5 or 6 levels.

http://www.moddb.com/mods/ruiner

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Alien Arena, the new 2011 version, free:

http://icculus.org/alienarena/rpa/