It's a little older CPU socket, so it'll be a little harder to find one new, but something like the Abit IS7 series or Asus P4P800 are a couple that should be pretty easy to find.
Also, since you have a Dell, know that---at least in the past---they have used power supplies that differ in pin-outs from regular power supplies. This makes them electrically incompatible with other motherboards, so you'll want to factor in for a new power supply. You can get a good one in the 350W range from Antec Enermax or Fortron that'll run between $30-50. Combine that with the cost of a replacement motherboard running $50-60 (or even less), you're looking at around $100.
Any motherboard with the Intel i845D/PE, i865 or i875 series chipsets will support that. They're not the only chipsets available, but they are going to be ones that you're most likely to run across.