It's rather specialized, but I'm on Steepster (http://www.steepster.com) a lot for tea. It's a ratings/review/tracking website. It also tries to be a social networking site.

For travel, Seat Guru (http://www.seatguru.com/) can help when you're picking out seats on an airplane.

For pets, Merck Veterinary Manual (http://www.merckvetmanual.com/mvm/index.jsp) can explain some conditions and treatments.