Depends on what you're looking for -
If you want easy setup go with Redhat or Mandrake as recommended by others.
I've been using Slackware for 6+ years now. The installation is much smoother now than it used to be, but it still would require a lot of work if you're not already familiar with Linux (and unix in general). OTOH, it would be a great learning experience. My first slackware install took the better part of a weekend to get everything working (this was back when most cards were still ISA non-PNP & you had to compile IRQ's/whatnot into the kernel). Frustrating at times, but very rewarding once you get your kernel built cleanly with everything working.
Make sure the version of XFree86 that comes with your chosen distro has support for your video card. The latest X release has support for Radeon & GeForce cards, but I don't think many distro's have bumped yet.
Whichever distro you pick, expect to do a lot of digging through doc's and asking for a lot of help to get everything setup correctly.
Fun right?
