I'm quite surprised no one has mentioned Kraken yet. You literally only need to type in your name and address to start trading. And you don't need to submit loads of paperwork to withdraw anything.
While I like Kraken, the topic-starter mentioned he is in the US and Kraken currently doesn't offer any USD deposits and while USD/BTC trading (and USD withdrawals) are technically still possible, USD/BTC volume is far too low to be of any use.
Kraken is great for EUR users, but until they finalize their banking and licensing affairs in the US, Americans better look elsewhere.