For Windows machines Only
I don't use CCleaner [ http://www.piriform.com/CCLEANER ] when it comes to registry cleaning because I'm not that techie and many tech experts tell you not to really mess around in your system like that because one misstep and you may need to do a reinstall or run your repair disk. But what I do use CCleaner for is when it comes to cleaning the temporary files, cache, history from my computer.
Whatever browsers you have installed on your computer (I have IE, Chrome, and Mozilla Firefox) it will search and dig into your system and get rid of the temp files when online. Yes, I set up all of my browsers to erase my history and other temporary files but you will be amazed what remains even when you perform that task.
How to use it is once you have closed your browser(s) {it cannot perform a full sweep until all of your browsers have been closed} and just click the button and that's it.
It's a small app and it's free but again, if you're comfortable using this type of tool I would highly recommend it.