Easiest way is go to go newegg.com and do some searching. The E8400 is LGA775 socket, so just go to Computer Hardware>motherboards>Intel motherboards>LGA775 socket. That should give you a great list of motherboards.
Most of the mobos are going to be very similar. Only difference are peripherals, size, and what type of north-bridges are on them. For example, if you want high end video cards in your motherboards, get one with 2 PCI-Express 16x slots (for SLI or Crossfire) or, if you want 16GB of RAM, find one that is compatible with that.
This is where you choose what you want, but be sure to come back to the forums here before buying. Let us know what you want and we can be sure that's what you need and that it will be compatible with what you're trying to do.