This is a cool site that lets you mine bitcoin using your browser and also offers free rolls - giving you a chance at $200 in Bitcoin each hour. The site also pays you 4.08% APR on your bitcoin balance of over $1USD, so it is a decent place to store and keep your BTC.
All you have to do is enter the captcha and click Free Roll and depending on your roll you will win some fractions of bitcoin every hour. Just take the free roll/BTC and let the BTC stack up. Also, you don't have to throw any of your own BTC at it if you don't want. You can slowly build it up until you hit the threshold to start getting the 4.08% interest. You can withdraw any time you like.