TripAdvisor is a perfect example of crowdsourcing. It relies on reviews of it's members to give more info about vaction spots, transportation, and trips. It is an example of crowdsourcing because it takes the input of thousands of people to give more info to others. The definition of crowdsourcing is "the act of outsourcing tasks...to an undefined, large group of people (crowd)". This sounds exactly like what TripAdvisor does.

http://www.callcentrehelper.com/ten-examples-of-crowdsourcing-14133.htm
http://www.slideshare.net/davidgracia/crowdsourcing-at-tripadvisor