Also in case it's needed, I'm probably going to crossfire 2 of these:
XFX HD-489A-ZDDC Radeon HD 4890 XXX Edition 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card.
This is my first system build, so could someone tell me what should I look for when buying a motherboard? The FAQ is mostly for troubleshooting and the "choosing right parts" sticky on homebuilt systems mostly list motherboards.