Anyone have advice on a good 64-bit LINUX version?

I'm a bit hacked off that VISTA 32-bit cannot recognize up to 4 GB of memory (which it needs to run well IMO), and I'm not inclined to shell out the wads of cash that MS wants for Vista 64-bit. It's been a few weeks since I played a computer game, and I am in the mood to experiment with my computer.

So, any of you geeks running LINUX boxes have a good suggestion or two? :-)