There are many factors when deciding which motherboard to purchase. Are you going to keep the same chip, and if so, what chip is it?? What's the pin set up (754, 939, AM2)? Additionally, it may take different RAM. Some mobo upgrades can run into some money, so make sure all the above criteria are met before deciding on a new motherboard.
Socket 775/EVGA 650i Ultra board/use one of the 1066FSB core 2 duos (best you can afford)ou would not hane SLI capabilities or 1333 FSB capabilities/concentrate on saving money using the older (but still excellant) Intel core 2.