To ship bicycles overseas, I used to use a fiberglass box. It has made some 40 trips now and it is cracked in many places. Baggage handlers have managed to bend the 1/2 inch steel rods inside and smashed all four wheels. I have also shipped bicycles in airline-provided cardboard boxes, which seems to work surprisingly well considering the damage to the fiberglass box. I always take off the pedals and the seatpost with saddle, on the theory that this makes it harder to ride it off. I also take off the rear derailleur and tape it to the frame, a bent dropout would be the end of the trip. The handlebars must be turned sideways. (Bring tools to do all this.) Always let most but not all of the air out of the tires or some physics-impaired baggage handlers might do it for you when you aren't looking. If you ship bicycles with the wheels removed, put spacers into the dropouts, you can get them for free from bicycle stores.
Recently I have been sending bicycles without a box because my tours began and ended at different airports. The airline usually requires you to box the bicycle in a cardboard box that they are supposed to have in stock but often don't. If they don't you'll have to ask other airlines or talk them into accepting the bicycle without a box. Bring a wide felt-tip marker to paint the destination address and your name on the side of the box. There is a risk of having wheels bent, paint scratched, and dents in the tubes, but so far I have been lucky. Allow at least one hour at the airport for boxing! Two in the US because they'll put you through some extra silly security checks. Believe me, you'll need it.
International flights allow two pieces of baggage, one of which may be a bicycle, if the combined weight does not exceed 36 kg. Tell the airline that you have a bicycle with you, some shuttle flights use small aircraft that don't have room for bicycles.
See also article for "Panniers"
