user1891: Up till now I know two websites where one can get free bitcoins:

http://www.bitvisitor.com/
https://freebitcoins.appspot.com
http://freebitco.in
http://takefreebitcoin.com/

Is there a comprehensive list of all such websites available somewhere?

user516: http://skude.se/BTC/ provides links to a number of websites that provide free bitcoins, but generally doesn't include sites it doesn't get a referral bonus from. It also provides a timer that helps you determine when you can revisit each site to collect more.
Another site providing a good list in a readable format is here:
http://bitcoiner.net/list

user2838: www.FreeBitcoinSites.com and www.squidoo.com/freebitcoins are a couple of good resources for places to get free bitcoins.

user2485: You can also check out this site: http://earnfreebitcoins.com

EarnFreeBitcoins.com is a website in which you earn small amounts of
  Bitcoins in exchange for visiting websites for a designated period of
  time. You may be required to spend anywhere from one minute, up to
  five minutes or more on the sponsored website. You must spend the full
  amount of required time on the website in order to recieve payment.


user1861: Constantly updated list: https://bitcointalk.org/index.php?topic=90718.0

Free Bitcoin sites:

The Bitcoin faucet.
One time payout per Google account. Explanation available at the site.
Daily Bitcoins.
Can be used once an hour now, and not just once a day.
CoinAd.com.
Can be used once an hour with registration.
Bitcoin Addict
Bitcoiner
Bunny Run.
See here for more info.
Free bitcoins - netlookup.se
Nakabot's Bitcoin Faucet
(Tor hidden service) NakaBot pays out a portion of its winnings in 0.001 increments.
Free BitCoin Daily Scratchcard
kickme.to/goxkeygen
MtGox account needed to redeem the code one receives.
bitcoinpixels.com
0.01 BTC free when signing up to betfair. See here for more info.
memorydealers
Learn how here.
Omnicoins
Learn how here.
cointicket.org
BitCrate *
bitcoins.so *
Roll dice : same numbers - win 0.01
Paperco.in faucet *
Scan a QR code to reveal a MtGox code for 0.0007 BTC.

Gambling sites that give out free bitcoins ( freerolls etc. ) after you join
Dragon's Tale
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
Seals has a free poker tournament every hour with a .05BTC prize. There are larger free tournaments from time to time.
See here for more info.
Strike Sapphire
See here for more info.

Not exactly Free but popular "earn" Bitcoin sites
BitVisitor
Earn Bitcoins for visiting websites
CoinTube.TV
Earn Bitcoins for watching TV

1891: <p>Up till now I know two websites where one can get free bitcoins:</p>

<ul>
<li><a href="http://www.bitvisitor.com/" rel="nofollow">http://www.bitvisitor.com/</a></li>
<li><a href="https://freebitcoins.appspot.com" rel="nofollow">https://freebitcoins.appspot.com</a></li>
<li><a href="http://freebitco.in" rel="nofollow">http://freebitco.in</a></li>
<li><a href="http://takefreebitcoin.com/" rel="nofollow">http://takefreebitcoin.com/</a></li>
</ul>

<p>Is there a comprehensive list of all such websites available somewhere?</p>
 516: <p><a href="http://skude.se/BTC/" rel="nofollow">http://skude.se/BTC/</a> provides links to a number of websites that provide free bitcoins, but generally doesn't include sites it doesn't get a referral bonus from. It also provides a timer that helps you determine when you can revisit each site to collect more.</p>

<p>Another site providing a good list in a readable format is here:
<a href="http://bitcoiner.net/list" rel="nofollow">http://bitcoiner.net/list</a></p>
 2838: <p><a href="http://www.freebitcoinsites.com" rel="nofollow">www.FreeBitcoinSites.com</a> and <a href="http://www.squidoo.com/freebitcoins" rel="nofollow">www.squidoo.com/freebitcoins</a> are a couple of good resources for places to get free bitcoins.</p>
 2485: <p>You can also check out this site: <a href="http://earnfreebitcoins.com" rel="nofollow">http://earnfreebitcoins.com</a></p>

<blockquote>
  <p>EarnFreeBitcoins.com is a website in which you earn small amounts of
  Bitcoins in exchange for visiting websites for a designated period of
  time. You may be required to spend anywhere from one minute, up to
  five minutes or more on the sponsored website. You must spend the full
  amount of required time on the website in order to recieve payment.</p>
</blockquote>
 1861: <p>Constantly updated list: <a href="https://bitcointalk.org/index.php?topic=90718.0">https://bitcointalk.org/index.php?topic=90718.0</a></p>

<blockquote>
  <p>Free Bitcoin sites:</p>
</blockquote>

<p>The Bitcoin faucet.
One time payout per Google account. Explanation available at the site.</p>

<p>Daily Bitcoins.
Can be used once an hour now, and not just once a day.</p>

<p>CoinAd.com.
Can be used once an hour with registration.</p>

<p>Bitcoin Addict</p>

<p>Bitcoiner</p>

<p>Bunny Run.
See here for more info.</p>

<p>Free bitcoins - netlookup.se</p>

<p>Nakabot's Bitcoin Faucet
(Tor hidden service) NakaBot pays out a portion of its winnings in 0.001 increments.</p>

<p>Free BitCoin Daily Scratchcard</p>

<p>kickme.to/goxkeygen
MtGox account needed to redeem the code one receives.</p>

<p>bitcoinpixels.com
0.01 BTC free when signing up to betfair. See here for more info.</p>

<p>memorydealers
Learn how here.</p>

<p>Omnicoins
Learn how here.</p>

<p>cointicket.org</p>

<p>BitCrate *</p>

<p>bitcoins.so *
Roll dice : same numbers - win 0.01</p>

<p>Paperco.in faucet *
Scan a QR code to reveal a MtGox code for 0.0007 BTC.</p>

<hr>

<h2>Gambling sites that give out free bitcoins ( freerolls etc. ) after you join</h2>

<p>Dragon's Tale
A casino site, but gives out small amounts for free that you can use to gamble with or withdraw to your own Bitcoin wallet.</p>

<p>Seals with Clubs
Seals has a free poker tournament every hour with a .05BTC prize. There are larger free tournaments from time to time.
See here for more info.</p>

<p>Strike Sapphire
See here for more info.</p>

<hr>

<h2>Not exactly Free but popular "earn" Bitcoin sites</h2>

<p>BitVisitor
Earn Bitcoins for visiting websites</p>

<p>CoinTube.TV
Earn Bitcoins for watching TV</p>
