If SDelete is a tiny scalpel, Eraser is an enormous all-in-one toolbox devoted to the same task. It's free, it comes with a beautiful interface, and it can do just about anything related to wiping files securely.
Eraser includes its own interface into the Task Scheduler, so you can set automated disk sweep schedules from within the application. Aside from wiping free space, Eraser can securely delete the contents of any folder on a set schedule. That sounds like a scary proposition (remember, there's no way to recover files securely deleted), but brave souls may appreciate having the option. Also, if you'd like to purge your recycle bin regularly and securely, Eraser can help you there.
Last but not least, Eraser integrates with the file context menu built into Windows: You can right-click any file or folder and get an Eraser submenu. From there, you can securely wipe the file or folder, either at once or the next time your computer reboots. All in all, if you're serious about wiping files regularly, Eraser is a very solid tool to use.
CCleaner offers two kinds of overwriting
Finally, no discussion of keeping your computer clean and tidy is complete without mention of famous freebie CCleaner. It completes a spectrum of cleaning options: SDelete is a minimalistic unitasker; Eraser is a bigger toolbox, but it still focused on file deletion; and CCleaner is a do-it-all tool that tries to rid your computer of many different types of bloat.
CCleaner scans your computer, looking for temporary files, browser cookies, and other information that can be removed without danger. Then, when you're redy to remove it, you can opt for secure file deletion. Unlike Eraser, CCleaner doesn't let you pick a secure deletion algorithm to use, but it does let you choose one of four levels of overwriting.
Most people would probably go with the Simple Overwrite option, which does just one pass; but if your information is very sensitive, you can go all the way to Very Complex Overwrite, overwriting your data with 35 passes. Making so many passes can be time-consuming, but that's a common trade-off with encryption and security: You can arrange procsses to be fast and comfortable, or secure and comparatively slow (or even cumbersome).
Like SDelete and Eraser, CCleaner includes a feature for wiping free disk space clean. It can't sort files, as DropIt and RoboBasket can, but in combination with one of those tools, it can o a great job of keeping your files orderly while securely disposing of things you don't need.