Crowdsourcing is such a vast and interesting topic! Where to start…
Crowdsourcing is basically asking people to help you do something. You could say barn-raising is crowdsourced construction.
Wikipedia is my favorite example of a crowdsourced knowledge base.
99 Designs is one of the bigger websites where you can crowdsource design work.
Crowdfunding is another example of sourcing money from others. Started with IndieGoGo and blew up with KickStarter. Now there’sStartSomeGood and ThrdPlace, to name a few more (because they happen to be LA companies).
And now there’s Crowdfinancing, which sources investments from the public to start companies. This is coming into play soon, with sites like Crowdfunder preparing for the big day the switch is flicked. (another LA company)
For anyone who wants to get after it, Wikinomics is supposedly a fascinating book.