Just FYI ........
I was in Comp USA yesterday and stopped to look at what they had on the shelf. Figured it was a holiday and all, they'd have more selection than normal.
They had 3 PCI cards. ATI's Radeon 9250 w/ 256 megs of RAM for 70 - 80 bucks (but thats only a DX 8.1 card), a Geforce FX 5200 w/ 128 megs of RAM for 50 bucks (DX 9.0 card but not much performance), and a Geforce FX 5500 w/ 256 megs of RAM for 100 bucks. The FX 5500 is the best bet, but as I said before its not really much of a card compared to the new ones, and it costs 100 bucks. But it would work, and maybe help you put off that upgrade for a bit.
My previous advice still stands as your best bet, but if you just want something to get you going NOW .............
They wont make any newer PCI cards. Thats as good as its gonna get.