Suggest travel sites

This time I would like your help! There are so many travelling and booking sites out there, and I would like to know a little about your travel process...

Which sites to you go to and use?

Why do you think these are the best? Do you use different sites for booking flights and finding hotels?

I personally use Kayak and I do have my own travel agent, who offers great deals, but I would want to know more website and explore. So if you have any suggestion for me, please comment and share your knowledge with me!