I just went through this with planning an upcoming trip. After looking at the various airlines, their baggage policies, their ticket prices, the cost of shipping the bike separately, the transportation issues that caused, the prospect of taking my bike apart to fit it in a box or paying someone to do it, I decided to take the train.
It certainly takes longer, and is not without its own challenges (and may not even be an option in many situations), but it seems like I can roll up to the station, buy a box for $15 that my bike will fit into with minimal disassembly, and put it on the train for $5.
This trip is still in the future, so we'll see how it goes, but I'm looking forward to it.
Your options are limited, and I think they've been covered:
S&S couplers
Folding bike
Ship separately
Find a bike-friendly airline.
Even a frame alone seems like it would be tricky. You can always measure and see if it would fit, and then it might work, but I have a problem imagining all my gear plus a bicycle in pieces fitting into two standard-sized containers. And, depending on the airline, a second, or even a first checked bag can cost you extra even if it's within the size limits.