DBAN is a great tool, it can almost guarantee that the data on the drive will be unrecoverable if enough passes are performed with sufficient entropy, even when trying to recover data with an electron microscope.
It's important to note that a 7 pass erase with the Mersenne Twister PRNG is recommended although in modern hard drives one pass is usually enough. It's also important to note that it can't be guaranteed to to remove all data on a faulty drive for obvious reasons, in which case physical destruction of the platters is necessary.
Also quite handy: Shred for Linux, does the same thing for individual files overwriting the footprint with psuedo random data. In Windows Heidi Eraser is a handy tool to do the same thing.