WiebeTech's standalone Drive eRazer does what it says

If you've already got the optical media wiper you need to rest easy, you'll probably be able to escape insomnia altogether after picking up WiebeTech's Drive eRazer. Granted, we've seen more elaborate solutions to this problem before, but this little bugger is compact enough to lug around and enables users to erase sensitive data from 2.5- / 3.5-inch IDE, PATA and SATA drives without requiring any PC intervention. The company claims that it can write data at a "sustained rate of more than 35MB/s," which means that your 250GB HDD would be clean as a whistle in under two hours. Best of all, the Standard flavor checks in at just $99.95, and if you're still nervous about someone finding something in nothing, a Pro model -- which is "capable of more than one pass with random characters" -- is available for $50 more.