Powerful syncing program GoodSync works locally, across the Internet, with online services, and with mobile devices.
Goodsync is one of the nicest-looking and easiest-to-use of the dozen or so sync programs I've tested. Installation is a breeze and defining jobs nearly so. The tabbed interface (one tab per job) is thoughtfully and logically laid out, though the tool tips that would get you up to speed quicker are missing for many controls.
The program has all the features you'd expect: bidirectional and unidirectional syncing, backup, file filtering, syncing of deletions and job scheduling. It also has one exceedingly useful feature you might not anticipate--the ability to tag a folder. This keeps you from inadvertently syncing to a like-named but different folder on a different drive if you set a job to run automatically when you insert removable media. You can also sync across the network but not to CD/DVD.
My only GoodSync complaint is marketing-related. The company hypes the product's ability to back up Outlook and Outlook Express, which it does, but only the way you would with any other program--by selecting the files and marking them for back up. There's no special wizard though the manual tells you where and what to look for.
GoodSync offers a limited trial for personal use. It's unfettered for thirty days, but after that you're limited to 3 jobs and 100 files per job--not really enough for most users. The $30 Pro version removes those limits and is required for professional and government use. It also adds free upgrades and support to the mix.
Users have noted similarities between this program and Allway Sync--for good reason. Though the look and feel is slightly different, the price and features sets are identical. Fortunately, unlike with other product categories there's no proprietary file format that can be used to entice you to "buy twice," so simply pick the one that feels right for you.