Buffalo, Fujitsu, Maxtor, SimpleTech and Western Digital - all offer portable 2.5" hard drives at up to 320 GB, but some still lack features to make backup and synchronization an easy process.
http://www.tomshardware.com/2008/02/12/portable_storage_redefined/index.html
http://www.tomshardware.com/2008/02/12/portable_storage_redefined/index.html