Project Gutenberg… putting books in the public domain online. One or two people doing it is good. Thousands are better.
Distributed Proofreaders: letting Internet users help proofread books. One of the coolest services I’ve seen online. I’m going to help out when I get some time. And hopefully people are good at rekognising speling and grammer.
Here’s an example of a benefit, courtesy of someone’s favorite television show.