A friend recently bought a Gigabyte Nvidia GT210 graphics card to put in his Mediaportal HTPC. He had been having problesm with TV3 and stuttering with his previous ATI card and eventually, after trialling my GT240, gave in . The NVidia card runs perfectly. The surprise was that he found a passive (no fan) version that only takes up a single slot. The card is a low-profile card and they have basically built the extra cooling fins etc up into the area above the card to make it the equivalent of a full-sized card... but no fatter.
He was also running an NVidia 8200 motherboard and, with this card, the sound worked through the HDMI straight away without any SPDIF bypass cables or anything.
I mention this partly because I couldn't find it anywhere on any web sites (including Gigabyte's) but I can vouch that they exist. He bought it from Robert at PBTech in Queen Street if anybody is interested.