How about simple tools like CCleaner?
I don't use it because I don't need it. There are a few simple rules which I use to keep my system clean:
a)Never install software etc. unless I really do need it. I don't want to have 30 different browsers/ media players etc. IE works fine for me so I stick to 1 browser. As for a media player I use iTunes because I have an iPod.
b)If I want to try out new stuff (software, games, etc.) or if I have to install something in order to help a friend out I always use a Virtual Environment.
c)Configure the software right after the installation and make sure it's configured the way you want to. That way it does what you want.
d)Keep the installed software up to date.
e)The most important one ==> Think first, then think again, then reconsider, then.....if you are convinced you really want to, give a mouse click.
By simply following these simple rules I keep my system clean and fast. It won't get slow or get clogged with trash over time. I don't have to do reinstalled either. The only thing I have to 'delete and replace' now and then is the virtual test environment. But hey...that's what it is for

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Greetz,
Rover