I gotta re-re-install Quake 4 at some point (I re-installed it about two weeks before I had to reformat my HD), story is shit but the gameplay is spot on.

I really wish it had sold well enough to get an expansion pack or something.

idsoftware.com/store
20 bucks though
oh, and steam has it too, but you'll have to deal with typical steam bullshit. I'd rather pay the 20 bucks personally.

If you buy it on Steam you can just use the .pak files for a source port and never open up Steam again. I would suggest the Ultimate Quake box, since it comes with the first three games (no expansions though, oddly).