The program BCWipe has tons of good features. It's not free, but has a demo version that should handle wiping raw devices.
You could also investigate the built-in "cipher /w" option. It's part of XP, so I assume that it'll be in Windows Vista/7. It'll wipe files or free space, and not an entire device, so it's probably not what you need.
And for my final, somewhat top-heavy, solution, you could install VMWare, VirtualBox, or some other Vm software and boot any small Linux LiveCD and do the classic UNIX device nuke maneuver:
dd if=/dev/random of=/dev/<device>
(That, or simply boot the LiveCD directly.)
Just remember that a simple "free space" wipe (several suggested programs here, including two of my own) may leave some recoverable data lying around. Google for a PDF titled "One Big File Is Not Enough" by Garfinkel and Malan for a really interesting 2006 paper on the topic.