Bitfinex http://bit.ly/BFX-Bitfinex -one of the best crypto markets and of course one of the few that support IOTA re-opens registrations.
The problem is however new account has to deposited (crypto or fiat) at minimum 10 000 USD equivalent before they can trade or offer funding. (After this initial activation, account equity is allowed to drop below this activation threshold without consequence).
Still Bitfinex doesn’t support USD crypto traders.
So, for Americans and small-middle investors Binance http://bit.ly/Binance-market can be the better solution