I've written about this before but I've told no less than 3 people today so I thought I would repost. To me, the 2 most helpful sites for figuring out how to get where you're going are Wikipedia.org and TravelMath.com.

Every airport has a page on wikipedia and there is a section called "Airlines and Destinations". It lists every carrier and each of their nonstop destinations. You can use this to find creative routing. Incidentally, I also use both of these sites for rebooking passengers. One of my most memorable was when I had a passenger who was going to misconnect in IAH to SFO and all the other flights were full. By checking Wikipedia, I was able to route them IAH-ABQ-SFO. The system is not going to look for flights like that. I have found lots of creative options for nonreving this way too.

Travelmath has many different calculators but the most useful to me is the one for nearest airport. You can pick any town and it will figure the nearest airports and separate by international and domestic. This will sometimes give you alternative airports if you're not familiar with the area.