I actually talked to Mauricio at sportsbook.com the other day and they allow adult traffic to their affiliate program,
http://www.commissionaccount.com/, which includes a few different sportsbooks. Honestly I believe most of them will.
If you wanted a book that I recommend and actually play at then go with 5dimes.com. They used to accept adult traffic, not sure if they still do but just e-mail them and they are quick to respond.
Are you just looking for books that take US customers?