The DFI Infinity is good. I put one into my friend's box a week ago. It was an NF2 Ultra Infinity, I think. Reasonable price and good features.
EPoX and MSI make very good boards too. Maybe an EPoX 8RDA3 series or an MSI K7N2 series. Note that MSI boards often don't have the four mounting holes around the CPU socket if you're thinking about ditching the noisy (to me) retail heatsink and going for a quieter aftermarket solution. EPoX boards usually do, but check with the heatsink manufacturer.
Get a board based on the nforce2 ultra 400 chipset. I think all the boards mentioned so far are. I like that one. Much less flaky than some past versions.
Are you looking for onboard RAID, firewire, dual ethernet, and/or SATA? If not, you can save $20-50 off by getting the less feature-packed versions. For example, the 8RDA3I lacks the SATA, onboard RAID, and dual ethernet of the 8RDA3+ but is otherwise identical and $20 cheaper. You find the same sort of thing with many other manufacturers.
Finally, decide if you want passive or active cooling on the northbridge. Abit often sticks those little video card-type fans on there and they're noisier than you might think. Some people mind, others don't. But for an HTPC, I'd shoot for one with a passive heatsink.
