https://bitcoin.org/en/
United States using nearly any payment method: cash, credit card, or bank transfer.
Coinbase
Popular
Coinbase is probably the fastest and easiest way to buy bitcoins in the USA.
If you need bitcoins fast, then buying with a credit card or debit card is a good option. Coinbase charges 3.99% fees for credit/debit card purchases but you can get your coins instantly.
Another payment option for US customers is using a connected bank account. The fees are less for this method–1.49%–but your coins are only delivered after five days.
Get $10 of free bitcoin when you buy more than $100 worth through this link.
https://www.buybitcoinworldwide.com/en/us/
http://www.coindesk.com/price/