Webroot Windows Washer is an efficient file wiper.

If you find yourself wanting to clean off the hard drive of your computer, one of the safest way to do it is to erase all the files in it and then record over them.
For Windows based computers, there are several programs, some free , some not, called "file wipers" that can do just that. Among them, the Wall Street Journal reviewed Window Washer from security software Webroot. It is a comprehesive security software that does more than just wipe file, it allows also for a more secure Internet surfing. It is not free and right now sells for $29.99 on the company Web site.
According to the Journal, " Window Washer does "bleaching" of files or complete wipe off so they can't be easily recovered, before you can rewrite something else on top of them.
For Mac users, there is a similar feature built-in the operating system of the latest versions and it is called "Secure Empty Trash".

For more, see WSJ.com