Wikis

Wikipedia is, of course, the most prominent example of crowd-sourcing. Many hands make light work, and even a couple of minutes out of a contributor's day adds up when you have hundreds or thousands of people working to spread the load.

I corrected some spelling on the Library wiki's Web 2.0 page (ironically, the word "collaboration"). Small stuff, but every edit (hopefully) makes the article better.

While Wikipedia is great for most topics, it has one drawback when it comes to in-depth exploration: notability. This requirement for a topic, person or character to be "notable" is particularly problematic for popular culture, which is why topic-specific wikis (such as the Muppet Wiki) can be far more fun to work with. My favourite wiki time-sink is TV Tropes, a wiki which is "a catalog of the tricks of the trade for writing fiction". It contains such topics as:
Spooky Silent Library;
The Library of Babel;
Scary Librarian;
Hot Librarian;
Magical Database; and
the Great Big Book of Everything.

But be warned! Tv Tropes is a Browser Narcotic; not only will it result in a tab explosion, but it will Ruin Your Life. Have fun :D.