For the most part, I tend to stick with ATI cards for HTPC use. Their audio decode is just plain better than NVidia and supports more formats which is a lifesaver when using the audio on the HDMI. Some of NVidia's cards still rely on the motherboards SPDIF connector for audio out (unsure of their audio decode on their latest and greatest models), and that can be problematic as all motherboards don't support full 5.1/7.1 out vis SPDIF with DVD/Blu-Ray/games.
Low end, a 56XX series with 512 meg DDR5 minimum. It has enough horsepower to do the DVD/Blu-Ray decodes and post processing. You can find a 5670 for ~$70 if you look around and watch for specials.
Full bore top end card, a 5870 if you need to play demanding games. Problem with big cards is power draw. More power = bigger power supply and more heat which is why I am partial to 56XX cards as they don't need any addiltional power besides the PCI-E slot and they are short enough to fit in almost any case.
The above is my opinion, and I could be wrong.
Edited by dpunisher, 05 July 2010 - 08:27 PM.
I am a retired Ford tech. Next to Fords, any computer is a piece of cake. (The cake, its not a lie)
3770K @4.5, Corsair H100, GTX780, 16gig Samsung, Obsidian 700 (yes there is a 700)