hello!
i've taken a bike abroad several times to mallorca, to france and to australia. when i first took a bike abroad i used one of those cardboard boxes that bikes/frames come in from the manufacturers. you will need to take the wheels out, skewers out of the wheels. sometimes, depending on the size of the box, you can leave the rear wheel in. make sure you deflate your tires!take the rear mech off also so if the box gets a clout it won't bend your rear hanger. take the seat post out. undo the handlebar pinchbolt on the stem. turn the bars sideways and underhook the bars under the top tube then ziptie the bars to the toptube so it's secure. i always covered every tube in foam pipe lagging (available from b&q etc). also buy plenty of bubble wrap (available from all garden centres). take off your pedals. i also took off my chainrings. put something between your rear drop out (if you have to take the rear wheel out) and in between the forks to prevent the rear dropouts getting crushed. i used a piece of wood cut to size and taped it in place. ziptie the rear mech to the chainstay on the inside of the stay. take off the bottle cages also. everything you take off the bike, wrap in bubble wrap plentifully. the bike should now be a secure unit with nothing flapping about. pop the bike into the box. place all the bubble wrapped parts in with the bike and tape the box up!
if you want to buy a bike bag, they are plenty around to choose from but i've never fancied them myself. i did, though, buy one of those a.b.s plastic boxes to take my bike to oz. these are the creme de la creme but also weigh about 13kilos. when your weight limit is around 22 kilos this takes up alot of your baggage allowance. although the abs plastic box was nice and is the ultimate protection the cardboard box has been the best way for me personally. especially as i was charged £80 extra by british airways for excess luggage when i went to oz then on the way back got charged AU$300 by singapore airlines to bring the bike back to UK!
if i go abroad again with a bike i will be using a cardboard box!
cheers,
cabledonut.