We did a tour this past summer in Eugene, OR (traveling from LAX) and ended up using a combination of shipbikes.com and bikeflights. We put two bikes (an MTB with road tires and a tiny fuji track bike with 650's) in one box and a heavy steel tandem in the second. The box with two bikes went via shipbikes, but the way the websites worked they wouldn't do the tandem so we sent it via bikeflights. Low hassle and inexpensive. I haven't tried flying with a tandem though. Maybe check over at Bikeforums.net (the flyertalk of bikes, also owned by IB)