There are in fact plenty of ways to obliterate the data from your drive. But excluding the violence that will not work if you want to keep your drive still alive and well-operating, you can use some of the following software and software-firmware methods.
Secure erase can be done in two ways – it can either be cryptographic or physical. The first one works for encrypted drives – program will simply remove the keys and then regenerate them, and it will make the info inaccessible. A physical erase will zap drive’s particles and then put them back into place. Before you start be sure to power down and disconnect all the drives you don’t want to be erased. Booting from CD or flash drive would be a better idea.
Parted Magic is a free to use but $5 to download Linux based program has several useful features like partition manager and file manager, and it can as well recover your data or erase it. It is simple and lightweight and applies for any drive, even USBs.
O&O SafeErase 7 ($30, free demo) is only for hard drives, and using it you will feel like a pro – there are options of removing different groups of information, or just wiping the whole disc. You can look for the specific sensitive files on your drive if you wish. It can wipe free space and the whole computer with drivers and all the data (but these expanded options are only available in the extended paid version).
Eraser 6 is an extremely simple and lightweight tool to clean folders and delete files to have more free space on your computer, and can be used on daily basis to keeping your drive as clean as possible. Be careful as the program does not have automatic selection of sensitive data, so being sure about what you are wiping is a must.
Active@ KillDisk has a free edition for Windows and can free space from folders to disc partition. But it as well does not have special smarts that would filter sensitive data or clean program cache.