I flew with a couple of bikes last year. Got (free? $20? i forget) cardboard bike boxes from the LBS - old boxes that their bikes arrived in from the mfg. I packed them with lots of styrofoam and newspaper and had no problems.

It wasn't nice and neat and I had to wrap stuff carefully, but it was cheap. That was good, cause the airlines charge a bunch to fly bikes - usually around $75 each way.