What do you use to erase duplicated files ?

[bench988]

I have been true believer of backups, but, not organized. Now I have lots of floppy (even 5 1/4" disk), cd and even backup files in the harddisk. Right now I am thinking of getting an extra 200G drive to just for the backups. When I copy all these files to 200G drive, there for sure would have duplicated files. So, what software you people out there use to erase these duplicated files ? There is nothing in the store you can buy. On the web, there are hundreds of this kind of utilities, just do know which one is simple and reliable to use, and I do not like to give out credit card number to purchase this. Any idea is appreciated.