Coinbase, BTC-E, Bitstamp and a pretty bunch of other local exchanges and options, This excluding local and personal deals like LBC and paxful which is actually becoming more popular than the traditional official website trading etc...
paxful is getting the attention because someone can make their own ad without depositing anything other than what is needed for the ad. search engines spit back localbitcoins and paxful and a person that wants to start using a site as more of a business than a client sees a $400 deposit at lbc versus $0 at pax