There are lots of third-party programs to carry out operations like checking the hard disk for errors, defragmenting, checking the registry for errors, etc. Many of them come in bundled software suites like Norton Utilities (now replaced by Norton 360). The problem here is that, if you decide to install lots of third-party tools to speed your PC up, your PC actually
slows down under the burden of having all of these extra programs installed!
You also have to be very careful when sourcing programs that mess about with your registry or claim to clear up your Internet history files, spyware, adware, etc. Many of these programs are either rubbish or they are adware / spyware themselves!
To be honest, I think that the drawbacks of installing lots of third-party tools like this outweighs the benefits. But, if you really, really want tools like this on your PC to automatically tidy your PC up for you, take a look at Norton 360 or Norton Utilities.
Hope that helps