Here is a short list that I have compiled, which showcases some popular sites where you can earn bitcoins.

peerbet https://peerbet.org/ : Earn bitcoins in gambling.

dailybitcoin.com Ad affiliate system :
The deal is, you make an account here (http://dailybitcoins.org/advertise/index.php), and then post your username on the bitcointalk forum here, (https://bitcointalk.org/index.php?topic=154216.0) , and 0.01 BTC will be credited to your account on dailybitcoin.com .

BitMillions (https://bitmillions.com/) - Bitcoin Lottery Earn bitcoins by sharing your custom affiliate betting address. Earn 20% of house fees for life. Our affiliate program uses a 60 days cookie. Affiliate earnings will be paid btw 1 and 5 blocks, expect real time winnings! Earning are sent without deducting any transaction fee! Banners provided for affiliates. More info at https://bitcointalk.org/index.php?topic=155027.0


Free Digital Money (http://www.freedigitalmoney.com/Bitcoins): Earn bitcoins by participating in sponsored offers. There are approximately 1000 offers available. Some offers are free and some require a purchase. Bitcoins are sent to you immediately after you participate in each offer. No account is needed to participate in offers.


iWantFreeBitCoins (http://www.iwantfreebitcoins.com/): Earn bitcoins by participating in sponsored offers. There are approximately 700 offers available. Some offers are free and some require a purchase. You receive a currency called BitPoints added to your balance immediately after you participate in each offer. Your BitPoints can be converted to bitcoins when you request a payout, which will be processed the following Wednesday or Sunday. The referral program pays 25% of everything earned by each user you refer. An account is needed to participate in offers.

Dragon's Tale (http://www.dragons.tl/)
A casino site, but gives out small amounts for free that you can use to gamble with or withdraw to your own Bitcoin wallet.

Seals with Clubs (https://www.sealswithclubs.org/)
Seals has a free poker tournament every hour with a .05BTC prize. There are larger free tournaments from time to time.

Strike Sapphire (https://strikesapphire.com/)

BitVegas (http://bitvegas.net/)
"For Minecraft lovers that want to get paid to play the game."

Rugatu Q&A (http://www.rugatu.com/):Get bitcoins by answering questions that other members have posted. A great way to do some freelancing job if you have an area of expertise and help support the bitcoin community. Sometimes higher value bounties are posted for programmers or media artists. You can login with your existing google, facebook, yahoo or openid account.


Bitvisitor (http://www.bitvisitor.com/):Earn bitcoins by visiting participating websites. Enter a bitcoin address to start visiting websites. No signup required. Each visit must last 5 minutes and requires entering a captcha. Payment is sent immediately after each visit. Website owners bid on how much they will pay for each visit.


RoyalBitcoin (http://www.royalbitcoin.com/): Earn bitcoins by sharing your custom affiliate betting address. Affiliates earn 1% of the total volume of bets that are placed through their addresses. Payments are made daily in BTC. No minimums or maximums, 1% is paid regardless of whether players have won or lost.


Bitcoin.de (https://www.bitcoin.de/en/registrieren): Every new user currently gets 0.01 Bitcoins for free. Affiliate program – users get Bitcoins for advising bitcoin.de to other users.
EarnFreeBitcoins Similar to Bitvisitor, you earn bitcoins for visiting websites. No signup, but you must visit each website for the specified period of time, and also enter a captcha in order to receive payment. Payments are queued to reduce transaction fees.


BitcoinGet (http://www.earnfreebitcoins.com/): Earn bitcoins for watching videos and completing tasks. No signup required. No minimum payout. Payments are made several times a day to reduce transaction fees.