I played with 2 options:
TrueCrypt and FreeOTFE
TrueCrypt has a Windows and Linux GUI making it pretty easy to use cross platform. It also do some pretty cool encryption of the boot drive to secure the whole computer, but I haven’t messed with that yet.
FreeOTFE has cool because it has a WIndows GUI and can automount under linux if you encrypt a whole partition as opposed to a volume (file) stored on a partition. I really wanted to go with FreeOTFE for the automounting, but ran into a deal breaker issue. Windows can only mount a single partition from a USB drive, so I couldn’t have a small partition to run FreeOTFE from (so it was portable to any Windows computer) and have a 2nd large encrypted partition for the data.
Configuring FreeOTFE and Linux see http://emcken.dk/weblog/archives/164-encrypted-usb-drive-in-ubuntu.html. My notes just in case the above link ever goes away:
sudo apt-get install cryptsetup
sudo modprobe dm-crypt ## If you haven’t rebooted
sudo cryptsetup –verbose –verify-passphrase luksFormat /dev/sdb5
sudo cryptsetup luksOpen /dev/sdb5 sdb5
# Based on fat32 or ntfs
sudo mkfs.vfat /dev/mapper/sdb5 -n “tpearsall”
sudo mkntfs -f /dev/mapper/sdb5
sudo cryptsetup luksClose sdb5