AT LAST!!
Kingston's DataTraveler DTVP Vault Privacy Edition flash drives work great with Mac OSX 10.4x and 10.5x. Make sure you're getting a DTVP drive; Kingston's DTV drives are not Mac compatible. The password protection is robust, as is the encryption, which uses 256-bit AES. On top of all this the drives are waterproof (to four feet), made of industrial-grade aluminum, and are fast as hell (on-the-fly encryption). For a User Manual, check out:
http://www.kingston.com/support/USBFLASHDRIVES/PDF/DTVaultPrivacyUsersManual_B04.pdf
By the way, the drives are 2GB, 4GB, 8GB, 16GB, 32GB, and 64GB. The drives have been expensive, ever since their May 2009 release, but prices are dramatically dropping now (I picked up an 8GB DTVP for $90).