I'd go with 7600 series, a 7600GS would be a good deliverer of graphx, if you want to spend around $40 more (or less) you could go for the 7600GT which i personally recommend, it has a reasonable better performance than the GS series...
My budget is around £550, not good i know but i only want to play some decent games and do the usual shit (internet etc.etc.) without my computer being useless in about a years time.
I could buy a better graphics card later on though. Those options dont seem to be available in the build schemes (on dell.co.uk)