Hi!
I am starting my PhD in SLA this fall. Well, next fall since I am deferring for the Fulbright ETA. There are roughly ten SLA/SLS/SLAT programs in the US.
Here are some good programs:
U of Hawai'i SLS
U of Arizona - SLAT (Second Language Acquisition & Teaching)
U of Maryland - SLA
U of Wisconsin, Madison - SLA
Please let me know if you have any questions, I'd be happy to help out.