Can anyone recommend a decent low-power PCI-E graphics card?

Must be able to decode HD video. Ideally it's also passively cooled or very quiet.

Doesn't have to be new, and TBH a slightly older model may help with Linux compatibility.

5570? I just installed one in an older P4 Dell Optiplex. The version I got came with half height brackets (hence why I got that card), draws power from the PCI-E slot only and ran fine using the crap Dell PSU (mild gaming for my nephew). It had a small fan but was very very quiet.

This one is passively cooled but has a slower memory clock http://www.overclockers.co.uk/showprodu ... ubcat=1699 "as well as accelerating ATI Stream compatible applications including a variety of video transcoders"

I've got a 5450 in mine. It's as low as you can go but it does everything I need (Photoshop is a bit slow) and allows me to mess with the HD video taken on my camera. http://www.overclockers.co.uk/showprodu ... subcat=168 "Supports 1080P HD movie playback "

A 5450 works decoding HD on my media centre.

or a 9600GT would do it. I've got some low power models that don't need the 6-pin connector.

They're rather quiet, almost silent if you put an Akasa cooler on them.