We used to have this debate every two weeks. Now, seems like we have it every week. My $.02:
I own both a Radeon 32 meg DDR and a GeForce 2 GTS Pro (32 meg DDR). I play tons of games from both my systems, and I can say with certainty that there is NOT a consistent, obvious difference between these cards. If there is, you have driver and/or tweaking problems.
My Radeon works flawlessly with every game I've tried (including the ones here where the author alleged incompatibility.) Both cards completely scream with Unreal Tournament, Q3 Arena, Half Life/Counter Strike/Team Fortress, Mech4, and other high-drain games. I can play all those games in high color at 1024 x 768 with absolutely no problem.
ATi did, in fact, have problems with drivers on SOME of its cards in the past. However, they have been incredibly aggressive in keeping the Radeon up to date, and in fact were the first major manufacturer to claim at least some compatibility with Direct X8.0 (which will kill most GeForce-based cards, by the way. As a side note: Do NOT upgrade to Direct 8 unless you have a compelling reason to do so. And believe me, you don't.)
All that said: I think both cards rock. My advice would be to buy whichever one you can find cheaper. I promise that if you spend an extra $50 for a GTS (or a Radeon, if that's how it shakes out) you'll regret it, because there just isn't that much difference. And yes, future, more advanced games may in fact give one card a clearer lead, but by then there will be a pile of 64 meg cards on the market that everyone will want anyway.
So, that's it for my rant. I'll let the idiots babble on now about cards they don't own.