If you can afford around $200 the GeForce 7900GS PCIe card is very
good, or for around $150(online and maybe some brick and mortar
retailer deals) GeForce 7600GTs PCIe are good. Both cards also come in
AGP varieties(if you need one), but you'd likely have to buy them
online and they'll likely be more expensive. If you want/need to go
cheaper you could likely even get away with a 7600GS which should be a
little over $100 online(this one also comes in AGP varieties and is
much more common). Performance of the 7600GS will be less than an
x800, but I'm not sure exactly where, best bet is to check on
anandtech.com and tomshardware.com for benchmarks, reviews, and anand's
Oblivion benchmarks...
The 7600GT is approximately equivalent to the ATI x800, and the 7900GS
would be approximately equivalent to a high end x1800 or lower x1900
models. I am currently using an(one) eVGA 7600GT KO (clocked @ CO
speed out of the box) and when I use Oblivion to bench it I get a high
of 45 FPS, low around 28 FPS with an overall average of 36 FPS in the
forest with HDR, distant lands, highest detail settings(basically all
highest except shadows which are at mid, win2k, CPU is AMD x2 4800+, 2G
DDR 400 RAM). Never bothered to go to a town or inside a building as
the forest area tends to give the lowest performance(other than
Oblivion gates) by far, and play feels smooth at those framerate
ranges.
(Oblivion makes for an excellent benchmark/system stability tool...)
Half Life 2 runs smooth as silk, but since I've just gotten it I
haven't checked the actual FPS on it yet... And those are the only 2
games I have that are recent enough to begin to stress my current
system setup.