I like to use Kayak because it give you every rate for the type of hotel, flight, car, etc. you are shopping for on every major travel site. It even includes the direct website of the hotel rates. What are other sites that are good and trustworthy?
Trivago is also another great site which anyone who loves traveling needs to familiarize himself/herself with. Just as with search engines, sometimes you might need to use more than one site to find the great deal which will save you a lot of money. Trivago is very much like Kayak but they focus on finding the best hotel for you.
I don't know why but I always end up going back to Expedia. They annoy me to death sometimes and you have to be careful because depending on what day it is the ticket price can be outrageous! But if you enter in the correct hubs for the cities you are looking at, then they atleast have a customer service dept that can help you after you make your purchase. They aren't so helpful once the airlines changes the flights however. They are only a search engine that can help you find existing prices. The airlines often make changes and then it is difficult for the customer service people to call and get help for you. I found direct calling through Skype to be useful though, and the people who help you find hotel deals will often give you an even better price than you will get online. So often times, I have gone online first, and then called their customer service desk to see if I could get it even cheaper.
Not doubt Expedia is useful and I also use it sometimes, but most of the time I use to consult the TripAdvisor and Yelp for more details about any region, flight timing and area location. I must say the traveler's reviews are most helpful to solve your problem even you can ask your questions there..
I use Opodo, Expedia, and Trivago to compare prices. I also use STA Travel which is a student site, but they get great deals. There is a card charge, but they offer a pass that allows you to change you return flight, which can be useful if you are traveling around and unsure of your plans. It can be worth it as I changed my flight to what would have been a high season ticket for a flat fee.