Once I understood what crowdsourcing is, I realized I have actually contributed to a website of this nature: Goodreads. It is a website where you can review and rate books that you have read, are reading, or want to read. A professor introduced me to Goodreads last year, and while I've slacked in adding new reviews, I wrote one today on Olive Kitteridge by Elizabeth Strout.
A nice feature with Goodreads is the widget that you can add to your blog. That way, readers of your blog can see what you think of current books. I'm adding a widget right now. Look for it on the right side of my page.
It is easy to add on to these websites; all you need is a membership (and those are mostly free). Plus, with websites like Goodreads and YouTube, a Google account works as your membership.
Are there other instances when you have crowdsourced?