Help me find Airfare Search Websites that are more detailed, please

Is there any website that offers more air ticket permutations than the standard airline sites and pages like Expedia, Orbitz, etc?

When shopping for tickets I have found different websites that are good at different kinds of searches but never one site that will search any way that I want it to.

As an example, let’s consider a current search I would like to try. Let’s say I am in NYC and I have a 4 month window to travel, I wish to visit 2 different cities (let’s say Paris and London) and I’m flexible about how long I’d like to spend in each (say, between 1 and 4 weeks), the order that I want to visit them, and the dates that I depart and return. IOW, I have a lot of leeway to change my schedule/plans in order to get the lowest airfare.

I fly on Northwest/KLM a lot and frequently use their website. It’s pretty good. For example, I can search for a roundtrip ticket 3 days in either direction of the dates that I enter–the prices are displayed on a 7 x 7 (I think) grid offering a lot of choices. But, this feature does not work if I have multi-city/open-jaw flights or have flights that originate outside of the US or Canada. And, I can’t check prices for NYC to London to Paris to NYC and have it ALSO check for NYC to Paris to London to NYC.

Of course I could check every possible combination with separate searches but there are thousands–if not more–permutations. I think that this is the same reason that ticket companies/airlines don’t offer such flexible searches–because it would take too much time and computational power to do so–but surely there is some way that I can let my good ol’ computer automatically perform all these different searches for me.

Any help? Has anybody written a meta-airline-ticket-search thingie that I can use? Is there already a website that does this?

Thank you.

http://itasoftware.com/
Click on “Looking for Airfares”, and then login in as guest.

Only problem is you can’t actually buy tickets from them–you have to either take their routing to a travel agent, or put the segments and times they come up with into one of the other sites and hope you end up with the same fare.