Free Commander is a great replacement for the standard Windows Explorer file manager. It is a dual-panel file explorer with many additional features. It has all the standard file management operations and it can be used to compare directories, display folder sizes, synchronize folders and more. It also has a build-in support for compressed archives, which you can look as a normal folder and search inside them. It has a FTP support which makes it more than just a file manager. Free Commander is freeware.

Homepage: http://www.freecommander.com