check with Kayak first. You can arrange things by very specific details as far as take off time landing time for both depature and return. Also you can scoop on either nonstop, 1 stop, 2 stop,red eye... what have you. Kayak tends to run a few $ more but once you find the cheapest flight on there, you can generally go directly to the airlines site and book it for much cheaper than anywhere else.
