Free Hide Folder
Sometimes the best way to keep people from prying into your personal folders is to keep their existence secret from the get go. That's easy to do with Free Hide Folder.
The program lets you make any folder (and all its subfolders and other contents) completely invisible with a just a little pointing and clicking. (And no, it doesn't just use the folder's hidden attribute.) The program is password protected so you're safe even if the bad guys know you're using the product.
It also lets you back up your folders' hidden states in case you have a system problem. And like the name says, it's free.