if you have a couple old hubs, stick them into the dropouts to keep your fork and rear triangle from being crushed. Or go to a bikeshop and get some plastic dummies that do the same thing- every new bike comes in a box with those things- very handy to have a couple on hand. Pipe insulation comes cheap from the hardware store and can protect your tubes from scratches and dents. Remove your rear derailleur from the frame (no need to remove the cable), wrap it in cardboard or bubble wrap and duct tape it to the chainstay to keep it from being bent. Don't be tempted to ship other hard items with it, anything rattling around in the box will damage the bike, although you can stuff some clothing in there for padding and cut down on your other luggage weight. Good luck- airport security can be brutal, be prepared to take it all out and repack at the airport. If you're afraid of the weight limit, curbside check-in can work wonders. The skycaps generally are much easier to deal with than the check-in people, especially if you give them a nice tip to help you out.
