Sites where you can earn bitcoins

CoinChat Earn bitcoins just for chatting.
BitVisitor Earn Free Bitcoins for Visiting Websites!
Earnfreebitcoins.com Visit websites in exchange for bitcoins.
BitcoinGet Complete offers and watch and get bitcoins in return.
Coin of Midas Visit websites in exchange for bitcoins.
Cointube Watch videos and earn bitcoins.

Sites where you can gamble

SatoshiDice Probably the most popular bitcoin gambling site.
Peerbet Bet against other players in provably fair games.
Kate Poker Play slots or poker for bitcoins. They offer two 0.03 BTC freeroll tournaments every day.
luckyb.it Provably fair bitcoin bets.
Betcoin Dice Provably fair bitcoin bets. High payouts.

Sites where you can buy and sell bitcoins

MT.GOX Mt.Gox is the world's most established Bitcoin exchange. Based in the US.
btc-e.com Bitcoin exchange based in Russia.
BitStamp Bitstamp is an European Union based bitcoin marketplace.
Vircurex An exchange that allows trading between many crypto currencies.

Online wallets

Blockchain The most popular bitcoin wallet and block explorer.
coinbase Coinbase is a bitcoin wallet and merchant platform.
inputs.io Send and receive bitcoins easily and safely.