Used to fly with my regular bike quite a bit and would just drop by my LBS and they'd give me a box from their last shipment of new bikes. I'd do enough disassembly of my bike to get it to fit in the box, take it to the ticket counter, sign the damage waiver form, and they'd check it through at no extra charge. Never had any problem with damage, but on a couple flights the bike didn't get on the same plane and was delivered later that day or the next morning.

But then many airlines (esp. on domestic US flights) started charging significant surcharges for bikes and other oversize items. So I got a Bike Friday folding bike which fits in a regular suitcase (mine's a Carlton) that meets the airline's 62" (L+W+H) rule. Still have to pay a little for having a checked bag on many airlines (SW is an exception), but it's much more reasonable than the charge for regular bikes.