There's very few motherboards that meet your criteria, and there's several that I wouldn't recommend, like anything from Epox, although the 9NPA+ series is your best bet for what you want and probably within your price range.
Jetway, Chaintech, and Soltek also have boards that'll do what you want, but I'm not sure of the availability or tweaking of these boards.
The DFI NF3 Ultra-D could work, but that's a pretty rare bird, so I don't know if you find it.
My opinion: Grab an nForce 4 board like the Chaintech VNF4 Ultra that's cheap and has some decent tweaks after you've saved the money to change to a PCIe video card.
If you went with a Socket 754 rig, you'd have an easier time, and quite honestly, if you're not going to go to Socket 939 and PCIe together, your best to stay with what you have or do an AGP/Socket 754 setup instead.