I think you're going to find that it doesn't matter what state you plan on moving to - all visas are issued by the State Department, which is federal. Though I have been otherwise horrifically unimpressed with the Obama presidency so far, you
might find the State Department a little more willing to accommodate your partner than they perhaps were a month ago. You should check out their website for more info -->
http://travel.state.gov/visa/visa_1750.html
EDIT: Hmm ... a little more digging turned up some disappointing info. Under the Defense of Marriage Act ... "The Federal Government may not treat same-sex relationships as marriages for any purpose, even if concluded or recognized by one of the states." I'm guessing this is going to pose a big problem in getting any sort of spousal visa through the State Department. Wouldn't hurt to talk to a lawyer, or at the very least, contact your US Embassy in London for options.