OnyX is a multifunction utility for Mac OS X (PowerPC and Intel). It allows you to verify the Startup Disk and the structure of its System files, to run misc tasks of system maintenance, to configure the hidden parameters of the Finder, Dock and of some of Apple's own applications, to delete caches, to remove a certain number of files and folders that may become cumbersome and more.
Unless of course you use OS X then you'll want to use -
Snow Leopard Cache Cleaner
Snow Leopard Cache Cleaner is a one stop solution for all of your OS X maintenance needs. Intel or PPC, Panther or Snow Leopard, sLCC has the tools to keep your system running at its best. sLCC Documents and the sLCC Engine maintain system health by providing full automation of common maintenance chores including virus scanning of internet downloads. The sLCC Engine can even repair permissions automatically after software installations. With the sLCC Engine, powerful system maintenance and antivirus can be completely transparent or as close as your menu bar.