Best bet is a cardboard bike box from your friendly local emporioum. Should cost you a bag of doughnuts or so! The bag option is good, and the bag may survive the flight and/or the conveyor belt, but probably won't survive the handlers. A box is much harder to throw around!
I have just returned from a week in morzine having taken the bike on the plane. Weighed up the pros and cons re. bag v box and opted for the neil pryde bag. I think as it was a good choice as we arrived at geneva in the rain and saw a box come out pretty soggy. The bag has enough padding but with added bubble wrap and spacers for the forks it worked great. Its not a cheap option but In my veiws it was worth it.
I got a bike bag from Ground Effect. It was really cheap (£45 incl. shipping and the Ground Effect tool wallet thing), packs up really small, and protected my bike (helped by a lot of pipe lagging and cardboard). It's now a little the worse for wear, but it'll still work fine, I'm sure.
I'm going with Alpine Tracks. I'm a bit worried as the tickets came through yesterday and the baggage allowance is only 20 kilos. Once I've wrapped my bike up that'll probably be 15 kilos. Guess I'll be travelling light!