When researching flights I usually try two things--www.kayak.com
which compares various search engines offering airline tickets, and I also go directly to the website of the airlines themselves, where I've often found better rates. However, budget airlines, like Easy Jet, Ryan Air, Air Asia, etc. are often not included on major search engines. Finally I found a site that includes them--keep this one for your files:
www.momondo.com
Another website I use frequently is www.tripadvisor.com to compare hotels. It contains reviews from readers with a point-rating system.
Buen viaje!
