A friend is doing the abbike Fast Ride Across America. Sounds like a good ride and well-supported. I would think that a later ride (this one starts end of April - Irivne California to Boston in 31 days of riding plus one rest day and 3400 miles) could get hot and less pleasant across the deserts and midwest.
That ride is perfect (maybe a little expensive), but I don't get out of school until the first week of May. Damn....