Compatibility

Options -
Cheapest - G31 chipset - Gigabyte GA-G31M-ES2L - Comes with onboard graphics

Both the below mobo require you to buy separate graphics card...
Next option - P43 - ASUS P5QL/EPU LGA 775 Intel P43, GIGABYTE GA-EP43-UD3L
Best option - P45 - GIGABYTE GA-EP45-UD3L, ASUS P5Q SE PLUS LGA 775 Intel P45

You can also check out brands like ASRock and Biostar...they would be cheaper but would have lower quality compared to the ASUS and Gigabyte...