Hitlist for Android helps you track flight prices for upcoming trips and alerts you when prices drop.
I've used both iOS and web based tools and now the Android app as well. I've saved at least $1000 a year myself on flights, mostly for vacation. I set the cities I want to go to, and the random dates I know I will be free...like this upcoming weekend and i get notifications about flight price drops. I've found $100 flights across the U.S, $300 flights to Dubai and $50 international Eurotrip jaunts from Hitlist.
Notifications of incredible flight deals
More work on social travel.