Here's another (SyncBack), but it's free.
Basically, just copies the files over to another drive or folder you chose, it examines the drive/folder, if the file is already there and unchanged it skips it. Lots of options depending on what you want to do and you just cant beat the price.
This is not OS backup software. Strictly data. I use it for my pictures.
http://download.cnet.com/SyncBack-Freeware/3000-2242_4-10413802.html


One of the drawbacks to many of the backup programs is the proprietary file extension that is automatically added.
I found a program that I really like and wanted to share the info with you.
It's from NTI and is called Shadow 4. It cost $36. It backs up your files in their native file format (no odd file extension), so you can easily examine your backup and drag and drop files from it, if you wish.
It's fairly basic and very easy to use. It has quite a few options you can set. I have it set to back up every day any changes I make to my documents, pictures or music. If I add, change or remove anything, it will be automatically mirrored on my backup drive. I've also set it to save the last previous state of each file, just in case I make a mistake.
For those who are doing complete hard drive backups, this probably is not the best program to use. For me, it does everything I want. I can set it and forget it, and be confident that my important files are safe if my hard drive ever crashes.