Here in the United States, our options for brokers are a bit limited. This is due to the rules & regulations for US citizens trading with margin / leverage.
Regardless, OANDA is a great option available for US citizens who want to trade currencies. It is regulated by the CFTC/NFA, which means your money is safe and third party protected.
This also means you won't be dealing with funny business with deposits/withdrawals, or price manipulation, etc.