I have used many sites for planning my journey including http://yatra.com, http://rediff.com/faresearch. But have just come across THE BEST site amongst all of them.
Its, ClearTrip (http://cleartrip.com). The best feature I like in ClearTrip is their "Best airfare calendar feature". Its so simple yet so much effective, it just saves your time. The workflow that they have used is pretty streight forward, I really liked this site. They also help in booking hotel, have not yet used their service yet (by actually booking tickets from site) but will surely do for my next travel. They have just caught me as their customer (unless I get very bad service!!)
Visit ClearTrip Calendar at,
http://www.cleartrip.com/calendar
Want to see the preview??
So, the price you see is for Bangalore - Ahmedabad direct flight's best price amongst all the flights on that day (I was just planning my next vacation! 
)
Thanks cleartrip for giving pretty neat and fast interface (they have also integrated AJAX; my User Experience was pretty cool with site!)
Stay tuned.. 