I've used CampBX for a few weeks without problems. Their customer support turnaround isn't great and can be frustrating, but they seem to be a legit business who is following the letter of the law with regard to FinCen.
one cool thing about them is their referral program. I have a referral link (every CampBX user does). Mine is
https://campbx.com/main.php?r=wvs48klhpI5You can click on it or not, doesn't matter to me. But if people sign up with your referral link, they get a slightly lower commission rate (wish i'd known this when I opened my account, i didn't get it) AND the person who generated that referral link gets a small kickback. Full disclosure, I think my commissions have amounted to about $2.50 (USD, not BTC!) so far. But still, it's kind of nice.
There aren't a lot of surviving US exchanges, so I'm sticking with CampBX until something changes.