Do a search for bestfares.com (probably this forum) and you'll find it gets mixed reviews. It seems the main problem is that the really good fares they advertise never seem to be available when you try to actually buy them.

I'd browse there for a while and then make up your own mind, but a lot of the stuff I've seen there shows up on FlyerTalk more or less simultaneously.

And, of course, there's no membership fee here.