Although CCleaner is not perfect, I find it to be a very useful tool when it comes to making more room on your hard drive within short time. It also has a Registry Integrity tool, Uninstall and Startup.
On the Cleaner tab, you can determine which files you want to delete and which ones you want to keep. You can also add custom files and folders to delete, making it a really easy task to keep your system in shape. You wouldn't believe how much space your Internet temporary files take! With its first run, CCleaner recovered over 400 Mbs on my computer. This is definitively a tool I will use very very often.
The Registry Integrity tool will scan your registry for problems and fix them. You can also choose what you want to include or exclude in the scan. It has happened to me that it marked for deletion entries that were actually right, so, personally, I don't trust the Registry tool very much.
You also have a couple of extra tools: the Uninstaller, that lets you uninstall programs from your computer (the program list loads faster than the 'Add/Remove Programs' tool from your PC's Control Panel). And finally, the Startup tool, where you can select and remove items that load when Windows starts, letting you have more control over your PC.
In the Settings tab, you will find some useful things like what cookies you want to delete, what custom files and folders you want to include or exclude, and also the type of deletion (normal or secure). You can save these settings to the .INI file to make sure CCleaner will delete what YOU want every time.