My colleagues who travel a lot fly with Ritchey Breakaway frames. They're full size frames that break down with not much effort.
To get the full benefit, you need the travel case. According to Ritchey, the travel case is small enough that most airlines don't require an oversize charge (but it's best to check first):
http://www.ritcheylogic.com/dyn_prod...9-202&k=472765
Disclaimer: Undiscovered Country is a Ritchey dealer.