List of Games That'll Run on Linux

Okay, so I'm not the biggest gamer (after all, I do run Linux) and I'll be the first to admit that gaming hasn't been a strong point of Linux operating systems with most games designed to run primarily on Windows then maybe on Macs with Linux a long forgotten afterthought.

However, I've noticing things are getting steadily better in particular with the gaming platform Steam beginning to accommodate Linux users. Here's a short list of the games you can run without a hitch on a Linux OS:

Besiege
Physics-based building game where you build medieval machines to achieve tasks, level villages etc.

Counter-Strike: Source
A classic and still very popular first person shooter.

Half Life 2 & Gary's Mod 
Great first person shooter campaign (HL2) and its sandbox spin-off.

CIV:V 
Incredibly expansive and complex strategy game.

I'll add to the list when and where I find them...

Edit:

Definitely worth checking the Steam Linux store for a comprehensive list.

In addition, a whole host of Windows games are playable with the PlayOnLinux addon.