I use this: Backup Your SD Card For Free With Media Card Sync | BerryReview.com »
It's free. Basically you point to a directory on your PC and it will sync files on your BB with that directory. Add files to one side and it will copy it over to the other. It requires a USB connection (but possibly Bluetooth will work), but it's a manual (click the button) sync.
The first time will be slow, especially if you have movies, etc. like I do. After that, it's very fast (unless you are copying new movies). The ONLY downside is when you decide to delete a file, you have to delete it on both sides, otherwise they will just re-sync and you have both files again.
I had to reformat my 4 GB SD card a few weeks ago, fortunately, I had sync'd recently and restoring it was simple.
Edit: This app is a bit 'dumber' than ActiveSync in this regard, as ActiveSync "knows" that a deleted file is "newer" than the other file and will delete the other during sync. This application, on the other hand, just makes the two directories equal, copying over missing files from one side to the other making both sides the same.