Yet another space where the internet should be able to make our lives significantly easier, yet somehow doesn't always deliver. Priceline, Orbitz, Expedia, all seem to make my travel decisions even MORE confusing. In theory the seem like a great idea, but few do one thing well, and few seem to deliver any value in the end. The one site that has really helped has been Kayak, and its mostly through its great User Interface. Fast searches across lots of carriers and easy date changing makes this a great way to find tickets. I can check Kayak quickly and regularly to get I'm happy with. Whether or not I'm getting a good deal, I don't know, and frankly havn't had the time to worry about.
Maybe that will change with the new generation of travel sites. Emily Chang's eHub has a very indepth review of the newest travel sites out there
Here's the full list, and I'll try to narrow it down for you: