ATI has announced new low-end cards, the Radeon HD 4350 and the Radeon HD 4550. The performance/watt and performance/$ look very good. I look forward to the open source drivers putting them to good use.
These would be great to put in one of my media PC's, just wish they would get a card that used 8w, but I guess that will never happen.
Back in the X1xxx days, soneone issued a radeon X1050 card. It was slower than toast. I hear ATI's on-board graphics chipsets (780, 790GX) are pretty good these days, but if you want an extra card I don't think that's available in that power envelope.