I personally like Allway Sync. Mainly because they have a PAF version that runs from my USB Key so I can sync stuff anywhere. I use to keep my Blackberry SD Card and my USB Key backed up to my DropBox Folder. It's Semi-Free (Freeware Version is good to sync up to 20,000 files in a month) Which is enough for my needs. You can use it to sync to a Windows Folder, and FTP Site or an Amazon S3 bucket if that is your cup of tea.

It can be found at Allway Sync: Free File Synchronization, Backup, Data Replication, PC Sync Software, Freeware, File Sync, Data Synchronization Software if your interested.