My first impression of cleartrip.com was a negative one -- their TV ad where a person sees a good looking woman in a bar and removes his ring so that he can pretend to be single (what's up with these brain-dead advertising folks? [*]) -- but a visit to their web site left a positive impression on me. Clear design, works fine in Firefox, an excellent summary page where you can mix and match flight options... what more could one ask for? Not to mention the fact that you can use said excellent summary page and identify the flights you want to take, and then mosey over to the airlines' own web sites and book your ticket, saving yourself at least a couple of hundred bucks <evil grin>.
[*] Before a certain commenter (I know who you are, BTW) jumps on me and calls me dumb, let me make myself clear: it's the inappropriateness of the wedding-ring-as-marital-status indicator in the Indian context that I'm ranting against.