Pike Packworks -
http://pikapackworks.com/ - highly, highly recommend it. It's small-ish enough that sometimes it can pass through the kiosk without any bike fees. Extremely easy to pack your bike as well and it feels very protected inside.
Stay away from hard cases as people mentioned, TSA always f things up when putting it back. It's also bulky and heavy.
Also, the Oru case might pack small but remember you have to take the fork off and literally stuff it in the bag. My gf used this once and I would never trust that bag to fit my bike - a 53cm.