Radeon 8500 Retail or GeForce3 Ti200? That's a no-brainer. Radeon 8500 stomps all over it, not just in IQ, but performance. Even the Ti500 is ousted by the Radeon 8500. You get superb DVD playback, incredible IQ, and all-out performance. ATi's latest driver sets are phenomenal (at least, in comparison to a few months ago). Did I mention BB has cleared them out for as little as $59 each (open box, of course, although I've heard of sealed retail's at 76.50 as well). Don't bother with the 128MB card. It's too much for too little, IMHO.
That said, you may be better off going with a cheap PCI card for now (as others have suggested) and waiting on the next generation, which will arrive sooner than most people realize. GF5 / R300 / Parhelia(?) are on the horizon and are likely to annihiliate anything today, perhaps significantly. Just my thoughts, YMMV.