You only lose a couple of FPS when using 8x slots, so a Crossfire setup won't be an issue.
If you really don't want to lose those FPS then you could look at the Gigabyte P67 UD7 which has a NF200 chip on it to bring you back up to 2 16x lanes, but it's a top-end board.
Pretty much any board made by Asus, Gigabyte or MSI will suit you very well, but make sure that the PCI-E lanes on the board are electrically 16x slots - some of teh cheaper Asus boards have 2 16x slots on them, but one of them is only electrically a 4x slot.
For the CPU, unless you are on a very tight budget then there is only 1 Sandy bridge CPU to choose for games: i5 2500K. You don't need the Hyperthreading that comes with the i7, but it's still an unlocked chip so you can overclock as much as you want.
If you don't want to overclock, then the standard i5 2500, or even i5 2400 will be just fine.