So I already have a fine enough PC for my general gaming usage, but I've really had the urge lately to A. Build something new and B. Try Linux. I know Linux isn't the end-all be-all when it comes to games, but I'd honestly be happy with just the Source games and the myriad of indie titles available. I really just want to do this so I can have a small, compact computer in my bedroom for light gaming. Plus, I'd get to learn something new which is always fun. :P
I don't have a set budget because I may not be able to do this for a little bit, but honestly, as cheap as you can come up with works. Remember, it'll mainly be playing TF2, L4D2 and Don't Starve, plus browsing the web. Plus, it needs to be as small as possible. My regular PC is in an Antec 300 case and that is way too big for this project.
Side note: I don't really follow Linux news, but has PC gaming gotten better at all on the OS? Just curious. :)