Agreed, you'd be fine with a very solid desktop card, and HD4850 is cheap and good, with native double precision capabilities for future GPGPU assist (still a long way off).
Even a GTS250 would be fine if you prefer the green team.
Depends on what options you have in your area.
Also any interest in multi-monitors?
I'm leaning GTS250 over HD4850 right now. The cards perform similarly, and neither one has GDDR5 or Dx11, so I kinda want the card with PhysX for $15 more.
Multi-monitors is a goal with this build. Hopefully gonna pick up an extra monitor at the end of the year/Black Friday sales. Monitor for the time being is a 1920x1080 21in. I want the extra one to be the same size and resolution.