You can go to the airline website and look up routes, not individual trips. They should have a schedule of flights in regular service listed. You could also try to find a TA to help out.
I did not have a fantastic experience booking as a group, but we did lock in our rates. Looking back, it was worth it, at least financially. I went with Northwest and was able to hold seats from Louisville, Kansas City, Detroit, Miami, and Philadelphia last year when the rates were low. I got my round trip seats for $480 and the same flight is now going for $979!
Look for Route Maps:
Continental Airlines - Route Maps
I will tell you that with the economy, direct flights are harder to get and are more costly.