Monolingual (clears unnecessary multilingual compononents language components for Applications and the OS)
http://monolingual.sourceforge.net/
MainMenu (run a large set of Mac OS X maintenance, cleaning and optimization tasks)
http://www.santasw.com/products.html
OmniDiskSweeper (track down files and folders that waste your hard drive space)
http://www.omnigroup.com/applications/omnidisksweeper/
Hard Disk Framentation info
http://www.kernelthread.com/mac/apme/fragmentation/