FoldersSynchronizer is bar none, the best synchronzing/backup tool that I've used.

I recently had a problem launching FoldersSynchronizer after my upgrade to Tiger 10.4 and emailed the developer. He was incredibly responsive and helped me over the course of about 3 days to identify the problem. He was even kind enough to send me an advance copy of version 3.5.1 to address the problem.

I've bought a lot of shareware, but Lorenzo at Softobe is outstanding. I would definitely recommend FoldersSynchronizer