Booking Buddy is another travel search engine that searches several travel booking agents including Kayak.com (my favorite), Expedia, Travelocity, Cheaptickets, Orbitz, Hotwire, Priceline, and more.

All you need to do is enter the travel information then click the travel provider on the right side to search.  The only downside to this is that you have to click each travel provider to search all of them.  I usually end up searching Kayak so why not go to Kayak.com directly?