CCleaner is one of the best freeware disk cleanup utilities available. Strangely enough, the program does not announce to users that it can actually be configured to run whenever (and as often) as you want via Task Scheduler.

To do this, you first need to configure CCleaner the way you'd like it to clean your drive everytime it's automatically run. I'd suggest disabling cookie cleaning and a few other things, as having those enabled will prove an inconvenience by signing you out of most sites after every cleaning. Once you've set that the way you'd like, navigate to Options>>Advanced and select "save all settings to INI file". You can now close CCleaner and open the Windows Task Scheduler by typing Task Scheduler into the start menu.

If it's not already shown, press the button to display the right-hand action pane. Once displayed, click "Create Basic Task". You can name it whatever you'd like. Something in relation to CCleaner would be ideal. Under trigger, select how often you would like it to run. I personally have it set to everyday at 5:30 PM, just so junk on my hard drive doesn't really have a chance to pile up. Under Action, select Run a Program and browse to the CCleaner executable, found in c:\Program Files\CCleaner. Make sure to add /AUTO as an arguement. Press next, and select Open the properties dialog for this task when I click finish. Once the dialog opens, select "Run with the highest privledges". Click OK and CCleaner will automatically run in the background whenever you selected for it to.

Note that this is for drive cleaning only, automated registry cleanup is not available.