If you are talking about the normal AMD 64 + series, then go with either SiS's chipsets or Nvidia's newest Nforce 3 chipset. I know that other people have reported problems with the bus bandwidth/speed of Nvidia's chipsets, but i have yet to notice anything going slow or wrong (even though it does take forever and a day to render with premiere). If you are wanting an Athlon64 fx motherboard, look at teh Sk8n. It is simply the best out there right now. It doesn't always win the benchmarks, but in pretty much every benchmark that it wins, it wins by a big difference, whereas when it loses, it loses by a small difference.
The real question to ask is what else will you do with this machine, how much money do you want to spend, and what processor do you plan on getting.