I've bought all but one of my sets of plane tickets through priceline. As far as you're a little flexible on what time you fly out (the one time I went through the airline, I had to leave at very certain times), they're great. I've generally paid 40-60% of the "retail" fare. There are some fees, but I don't think they're exorbitant... I seem to recall it being in the neighbourhood of $30 with 9/11 fees and such.

Edited to note: Everytime I flew I went out between 10am - 5pm... I think you will always fly out between 8am - 10pm unless you check a box saying you're willing to take a red-eye (and likely get a cheaper price)