If you are trying to build a system, start with the easy choices. Hard drive (SATA3), PSU 750 or 800, case (I like the Antec 600 and 900), and video card. The harder choice come with picking the CPU. The reason is the rest of the parts are specific to this choice. When I built this spring it was between the i7-2600k and the current AMD Phenom x6. Which ever way you go the MOBO, Cooler, and RAM are specific to that choice. Once you decide on the CPU, look at the Mobo's. When you have that, go to the Mfg's website and find the RAM's they recommend a pick from that.
...and tada...you have a system ready to buy and build. No compat issues.