research, lots and lots of research, it depends on what you're going to be using it for, if its just internet browsing, something with a single pcie 2.0 slot and a few pci slots would be fine, if you want a gaming rig, you probably want something with two or more pcie 2.0 slots, wether you want sli or crossfire, if you're doing a server, probably having one or more pcix slots