The Drive eRazer Ultra by Wiebetech is a standalone device for securely erasing hard drive data. It works natively with SATA and IDE/PAT drives, clearing them by overwriting every bit with a 0—there's simply nothing left to recover from the plate.
The process is relatively speedy, averaging about 7GB/min for newer drives. Its Secure Erase mode—one of many available, including user-generated programs—eliminates data left at the end of partly overwritten blocks, directories, partitions, and Host Protected Areas. And unlike, say a degaussing machine or a comically-large magnet, the drive remains usable afterwards. More here.