You can create bootable EBS volumes that are formatted with the XFS filesystem, allowing you to “freeze” the filesystem, call the ec2-create-snapshot command, and the “unfreeze” the filesystem. This way you can create a consistent, bootable snapshot of the live-running instance.

Here’s my article explaining how to do this:

http://www.shlomoswidler.com/2010/01/creating-consistent-snapshots-of-live.html