If you are unfamiliar with what the Windows registry is, it is not generally advisable to use a registry cleaner as the risks for inexperieced users are too high compared to the possible gains.
The registry is what keeps your computer running, it tells the computer what to do when certain events happen. However, during use, a lot of unwanted and unnecessary informations makes it into the registry mainly through installing and uninstalling programs or updated versions of existing programs. This gradual accumulation of unneeded or incorrect information can over time, slow your PC down
A registry cleaner tries to get rid of this unwanted information and restore your PC to full speed. The problem is that the cleaning process is less than perect. In particular there is always a small risk the registry cleaner may incorrectly remove information that is actually needed. In the worst case your PC may become unusable as a result.
That's why it is absolutely essential you backup your registry before using a registry cleaner. For most users the easiest way to do this is to create a system checkpoint. An even better way is to use a drive imaging program to create a snapshot of Windows which you can use for system recovery if needed.
This ever-present risk of problems is why the "best" registry cleaner is the one that causes fewer problems rather than the one that finds the greatest number of registry errors.
EasyCleaner [1] is my top recommendation. It has a good history of not creating problems and has a regularly updated list of registry values that must not be cleaned under any circumstance. It will also detect and delete duplicate files and clean up all your temporary files to clean up more disk space but this should be seen as a bonus rather the primary function of the product.
Eusing Free Registry Cleaner [2], is also a good program but doesn't have the features that EasyCleaner has. However it has a reasonable track record.
Another option is a program called RegSeeker but it has caused many problems to many people and cannot be recommended.
[1] EasyCleaner
Website: http://personal.inet.fi/business/toniarts/ecleane.htm
Download Link: http://personal.inet.fi/business/toniarts/ecleane.htm
Author: Toni Helenius
Current Version: 2.0.8.306
Download File Size: 2.81 MB
License: Freeware
Operating Systems: Windows 95-Vista
Additional Software Required: Windows 95 Only - Winsock 2 Update from microsoft.com
Other Languages: Many, see website for details
Other Information: None
[2] Eusing Free Registry Cleaner
Website: http://www.eusing.com/free_registry_cleaner/registry_cleaner.htm
Download Link: 5 Download Sites accessible from Website.
Author: Eusing Software
Current Version: 1.6
Download File Size: 890.8 KB
License: Freeware
Operating Systems: Windows 95-Vista
Additional Software Required: None
Other Languages: Many, see website for details
Other Information: None