Quick Erase is a simple tool which can overwrite and delete confidential files so they can't be recovered at a later date.
The program is unusually easy to use. All you have to do is drag and drop your chosen files onto the Quick Erase window (which by default remains on top of all other windows for convenience), and after confirming that you really do want to delete them, they'll be securely wiped.
And yet, despite all this simplicity, Quick Erase is surprisingly thorough. By default it will overwrite your target file 23 times with a complex series of bit patterns, renaming the file as well and resetting all its file times before the final deletion: no-one's going to recover anything useful after all that.
Of course this does also take a while, but fortunately the program allows you to choose from no less than 12 secure erase options. The quickest will overwrite the file just once, but even that's good enough for most purposes (check File > Options to see the settings available).