Like I said before, I have no experience with ATI cards other than what my friends have told me from their use, and from reading comments on message boards.
So all I'll recommend are nVidia.
As far as a PCI-E card is concerned. For under $150, I'd recommend this:
XFX PVT84JYDF3 GeForce 8600GT 512MB 128-bit GDDR3 PCI Express x16 HDCP Ready SLI Supported Video Card - Retail $129.99 + $5.84 shipping ($99.99 after $30 MIR).
-Elo