I believe tradehill would be what you are looking for.
TradeHill is based out of Chile.
I think campbx is going to be a new one from a thread I just read as well.
Their site says they are a company out of Atlanta. I don't see any FBN/DBA or company name registered for Camp BX yet but at the same time they aren't yet open so that's no reason to doubt that.
These are markets (trades occur when there is a match between bids and asks)
Registered LLC in California
Registered in Alabama
There are other fixed-rate exchanges (i.e., price is relative to price on a market elsewhere) in the U.S.:
(apparently Reston, VA)
Registered LLC in Florida
(apparently in Miami, FL)
You might find a local trader in the U.S.