I'm trying to plan a trip to Vegas in December. What site has the best deals?
Well, it depends on which country you wanna go. If you want to visit China, you are advised to book a tour with China Highlights, let's take Shanghai travel (http://funadvice.com/r/168r8b5cikk) for example, you can browse all the detailed information online about you China travel.
Tripadvisor & yahoo travel offer some of the most advanced trip planning features...though I've always used expedia myself.