There are a variety of registry tools available on the Internet today. Here is a small list of some of the free options available. WARNING: MODIFYING YOUR SYSTEM REGISTRY CAN CAUSE YOUR SYSTEM TO STOP FUNCTIONING! At this time, I have not experienced any significant improvement to systems by using these tools, nor have I extensively tested these tools, although I have tested them on my own system. Remember that any changes you make to your systems are AT YOUR OWN RISK! I offer NO WARRANTY EXPRESSED OR IMPLIED regarding the information contained here. If you need help regarding cleaning, securing, and/or maintaining your computer systems, please don't hesitate to call.

Auslogic's Registry Defrag - This tool defragments your system registry.
http://www.auslogics.com/en/software/registry-defrag

Eusing Free Registry Cleaner
http://www.eusing.com/free_registry_cleaner/registry_cleaner.htm

MV RegClean - This software is from Brazil and so it may be a little difficult to download. However, there is an English version, and I have had a client report significant improvements to their system performance after running this software.
http://www.velasco.com.br/softwares.php

NTRegOpt - (From snapfiles.com ) NTRegOpt is a registry compactor that improves system performance by compacting the registry, removing any slack space that may be left from previously modified or deleted keys. The program does not modify any registry entries, so it is safe to use. Also supports commandline switches for unattended runs.
http://www.larshederer.homepage.t-online.de/erunt/index.htm

Regsoft's Free Window Registry Repair 1.2
http://www.regsofts.com

RegSeeker - This is a zip file download which means that it does not require installation. You'll need to extract it to a folder and then run it from within that folder.
http://www.hoverdesk.net/freeware.htm