FareCast.com
I have been evangelizing this website to every man and his dog! I can't believe websites like Twitter are getting more attention than useful, smart websites like www.FareCast.com ! Weird!
Anyway, what's the one thing you worry about when you are planning on buying tickets for your upcoming vacation? Ticket Prices and/or When to buy them to get the best deal. Right?! This problem for most part has been solved by this awesome company called Farecast!
It's very simple and elegant. You punch in the dates that you want to depart and return, select if you'd like to compare with other websites and voila you have your results with a recommendation and a graph showing you some price history. Simply elegant!
My only problem - When it's time to buy, it actually takes me to another site, usually the airline site. I wish they integrated the buying aspect as well. None the less, it's a great site.
And, oh! You can also use their farecast prediction service for hotels! (Still in Beta) Aweeeeeesomeeeeeeeeee!!!
Happy traveling!
-Mithun Dhar