The other thing to look into is hotwire and priceline. A co-worker of mine's grandmother passed away last week, and he found that hotwire's price beat anything else he could find.

That said, make sure that you allow enough flexibility when you put in your dates, since you can't choose your flight times (i.e. if you need to be there saturday afternoon, don't count on getting a saturday morning flight, look at friday instead, etc)

However, since you're not really looking at last-minute travel here, it's not clear these options are the best for you... I've found that farther away from the dates, hotwire seems to just mirror the best fares on orbitz, etc...

Dan