File Synchronizer is an easy to use free software to synchronize data between 2 folders. You can specify any 2 folders that you want to synchronize. File Synchronizer will then compare and analyze both the folders, and clearly show the differences in a split pane view. Then, you can chooze the type of synchronization that you want to do.
File Synchronizer offers many options to sync folders. You can choose to simply copy all the data from one folder to second folder. Or, you can choose to synchronize the folders based on the files that are missing in each. Apart from these, File Synchronizer also offers some interesting synchronization options, such as if both the folders have file with same name then take the one that is latest, and copy that to second folder as well.
File Synchronizer is a good way to keep multiple folders in sync. If you want to keep multiple folders in sync across different computers, you can try DropBox. If you want to actually get rid of multiple copies of same file on your computer, you can use Duplicate Cleaner.