Binance has announced they have listed IOTA on their exchange. Previously the only real place to buy it was on Bitfinex which has banned US citizens.
Here is the announcement from their website:
Dear all,
IOTA/BTC and IOTA/ETH trading pairs are now available on Binance. You can start depositing and trading IOTA now.
Special Reminder:
Deposit IOTA only accept to the latest APP version.（iOS Download、Android Download）
IOTA deposit addresses should not be used more than once. After the first use of a deposit address, subsequent deposits to the same address will not be credited.