If you're based in the US, you have 3 options.
Coinbase:
https://www.coinbase.com/Link your Bank and Credit Card for instant purchases. You'll have to get to Level 2 before you can instant buy at certain amounts. Takes a few days to get verified for bank.
Circle:
https://www.circle.com/enSimilar to Coinbase, use either Bank or Credit Card, no fees, doesn't have the level system Coinbase has.
LocalBitcoins:
https://localbitcoins.com/Don't have to get verified, but buying Bitcoins here is usually at a premium or markup price. Have to find trusted sellers with lots of history. Can be done by variety of methods: Bank deposit, Paypal, Western Union, Dwolla, Moneypak, Venmo, Amazon Gift Card, or the recommended way in person in cash.