As someone who’s made my share of flights with tons of computer gear, I know good cases when I see them, and there aren’t many people who do it better than Pelican. Pelican has a new case purpose-built for 24-inch iMacs as part of its Case Cruiser line.
The box is made or reinforced plastic with layers of shock-resistant foam inside, built around a shell made purposely for the iMac.
If you fly and need more than just your laptop — say for demos at a convention — then have a look. Otherwise, well, don’t.