With X58, SLI is no longer constrained to nVidia chipsets. Most X58 boards will do SLI.
Gigabyte makes very good boards, and as long as you don't want 12GB of memory, you can nab the
UD3R for $200. Stepping up to the
UD4P will give you the full 6 memory slots and a bit more to work with in terms of expansion slots.
EVGA's latest board, the
141-BL-E757-TR is also an excellent performer with some killer looks, and reasonably priced to boot.
I'm using
ASUS's P6T Deluxe V2, and I've been liking it a lot. It's easy to overclock and has been rock solid stable for me. Of the boards I mentioned, it's also the only one that gives you extra room between the first two PCI-E x16 slots. This means that if you're going SLI with two double-wide cards, they won't be sandwiched so close together that the top card has trouble sucking in enough air to stay cool.
There's a number of other boards, like those from Foxconn or MSI, that are on the lower end of the price spectrum, but I have no idea how they stack up.