Dont know about individual files, but for wiping a disk when you bin/sell a pc there is KilLDisk. So there prpobably exists similar ones for individial files (i believe some security suites (symantec corporate does i think) have a secure "file-shredder" mode to try and delete things so they are very hard to recover

I think you are confused though "Leaving no bytes of data taking up HDD space". Thats not how a PC works. Each block on a hdd has a flag saying whether it is deleted for not. If it is "deleted" then that means that the pc can use that space for other things. Thats why its so easy to recover, as its not actually physically gone until something else gets written over where it used to belong.

I like and use Windows Washer by Webroot. It does harddrive Bleaching of files. You can wash file slack space to remove parts of old files. That is the files and data that gets left behind after Windows does its deleting process. It uses military grade bleaching and no one is able to get your files back because there is nothing left to get back! It is reasonably priced too. I use a few of there products and they work well. http://www.webroot.com/En_US/consumer-products.html
Oh by the way you can search the web for promotion/coupon codes for their products and get a nice discount too.
Anyway check it out and you be the judge.

Well, thats not strictly true. Due to the nature of magnetic media, nothing can ever be 100% securely deleted. Thats why the DoD physically smash the hard drives with hammers as well when they are to be disposed of.

Handy little file-shred utility... used before with good results.

Alternatively a good but not free encrypt-and-shred utility.

Nothing is fool-proof short of completely destroying drive (despite what you might ee on TV), but both pretty solid options