Zooniverse has quite a few neat projects using crowdsourcing of interested human brains to help scientists classify data.
They started off with Galaxy Zoo, which basically gets people to help classify what stars, solar systems, etc, and expanded out to quite a few more.
With Bat Detective, you listen to batty squeaks of doom, then help classify them.
All Zooniverse's stuff is really well done, and fun to use, while Contributing To Science at the same time. Give the squee-bats (or the other stuff) a poke, and you'll see!