fx5800 = 128-bit memory interface (had to have 1Ghz memory to offset) = dont get it!!
fx59x0 = 256-bit memory (good) 4x2 pipelines, but not as efficient
9800/9700 Pro = 256-bit (good) and 8x1(better) pipelines
the 9700/9800 Pro are the fastest cards available right now (if you can afford it)
I personally think the best price/performance is the 5900XT.
Here's my long list of cards I would NOT buy:
5900 ultra, 5800 U or 5950 U - too expensive, for price I would get a 9800pro
5700/5600 - almost the same as ti4200 and only slightly cheaper than 5900xt
9600 xt/pro - same as 5700, marginally better than a ti4200
5200/9100, etc... - crappy budget cards
So that really only leaves:
5900xt, 9700 pro, 9800 pro or 9800xt (and soon 6800)