How can I keep a folder backed up online with continuous syncing? I've found that the dropbox support for Titanium Backup never works for me amd I've also tried using ubuntuone and idrivesync but neither of these support setting a directory to keep in sync. 

Does anyone know of a free service, that can keep any directory of your choice backed up online? 

The best would be a scheduled task so that the battery isn't drained by continuous sync.
You can use DropSync. It can sync any specified folder and you can setup a schedule. Recent update of free version of the app removed limitation for the schedule.