I think some people on here obsess over the power supply a bit. I mean, it is absolutely essential to get a good one, but there are plenty of good ones to choose from. As long as you're getting a reliable model that can handle your system, the specifics don't matter as much. I think the motherboard is probably the most esential part of a system, because it has so many more different choices than other components. Depending on what sort of computer you want to build, you need to look at socket type, number of RAM slots, number of SATA/PATA ports, PCI slots, PCI-e slots, SLI/Crossfire support, and more.