Select a p45 for ddr2, or an x48 model for ddr3. Many of the low end stuff like foxconn or ecs will work fine if not overclocking. Newegg should have some p45's for around $75. They even had a foxconn x48 for $75 recently, a bargain.
Choose the chipset first. I went to P45 because it's less power-hungry than nVidia and its process is more recent than X48, so it boasts real overclocking potential - I still haven't raised voltages and already run at +33% Cpu and Ram).
Then, I chose ddr2 because the P45 then allows 16GB instead of 8GB with ddr3 - not brilliant, is it? And not even on every mobo!
And then, decide how many Pci-E you want, and whether two wide ones - and choice gets narrow enough.