For an HTPC GPU I would recommend a GT 520, preferably with passive cooling. That card supports all current features/techs and is capable of some pretty nice looking post processing on 1080p video. We've got one for $26 after rebates on Newegg right now, so that would be the way I'd go:
Newegg.com - Galaxy 52GGS4HX9DTX GeForce GT 520 (Fermi) Silent Edition 1GB 64-bit DDR3 PCI Express 2.0 x16 HDCP Ready Video Card