For a tour, if I want take a nice guitar, I borrow my friend's Calton case and check it - they're impossible to break. Did it twice with my favourite X175 on transatlantic flights without any problem. I really want a Calton case of my own one of these, trouble is they cost almost as much as a guitar!
For one-off flying gigs, I take my "cheap" guitar (modded DeArmond), in a regular case, and check that - did it lots of times, and surprisingly, no problems either. (save for the odd airline who want you to pay a little extra for oversize luggage)
They usually let me take solidbodies on board, and once or twice I've taken the neck off a tele or danelectro and put it in my clothing case that way.