Suggestion #1:
Consider flying a low cost carrier closer to the East coast of the US. For example Southwest out of Midway (MDW) to Philly (PHL) and then another carrier (US Airways) to Birmingham. It's slightly cheaper. I'm not sure if Jet Blue flies into Chicago and if so which of the airports. Southwest can only be booked on the web through southwest.com.

Suggestion #2:
Consider flying into London and taking a train. I found an Air Canada flight from ORD to LHR (connecting through Ottawa) for $869 on Orbitz.

Suggestion #3:
Signup on any airlines website for a frequent flyer number and their email specials. Some of them let you choose destinations so your email solicitations are more limited to what you want.

Suggestion #4:
Priceline.com. I've used this domestically, it's particularly beneficial when you are flexible on dates as you have indicated. If anyone has used it internationally it would be interesting to hear their input as well.

Suggestion #5:
Check the airline websites. The ones you mentioned are good, but they get a limited number of seats from the carriers. I've found instances of being able to go to the carriers website and get a cheaper better for me flight.