I have stayed away from ATI cards for some time (I used to have a Rage fury II that hated me) but I have to say that the Radeon 9700 is by far the better buy. The nvidia Geforce FX 5800 is only a little bit better performance wise, but is more expensive, takes up an extra PCI slots, and apparently is loud as heck. Also if you aren't going to be buying one for a while the Radeon 9700 should go down in price when the new ATI cards come out (which will be this summer, I think).
On a side note, the All-in-Wonder Radeon 9700 is pretty good; especially when you consider that it is only a little bit more, but includes all kinds of extras.
-Kurn