I've used a Giant bike bag that I bought for about 15 dollars. It's just a thin but tough cover that has straps to tie things up and most helpfully a shoulder strap so the bike can be easily carried. I wrap the whole bike in a sheet of acoustic foam that they sell at home improvement stores then I slide the bike bag over it. The bag folds up into a little 5"x 4" ball that I carry with me until I fly out, I just buy a new sheet of foam to repack. Not as protective as a box but so far I've haven't had any damage to the bike. In this configuration the bike also fits easily into the back seat of a normal cab. Being able to carry the bike along with my other luggage is a huge plus, I've traveled with a bike in a box and it is a nightmare trying to drag it around to/from airports with my other stuff.