Your Uninstaller! 2008 PRO is the best uninstaller program. It can search for registry settings, files etc., created by a particular application, and then remove it completely. There is an "AutoFix" button. It can search for invalid uninstall information and delete/correct it. It cannot search for invalid registry entries caused by a previously uninstalled program though. This is one drawback.
It also includes tools to clean up the internet browsing history, start menu history, etc. It also includes a Disk Cleaner that does the regular PC file cleanup (by deleting temp files, backup files, etc). After scanning, it automatically deletes all to the recycle bin. We also have the option of setting the start-up programs. We can even uninstall the Windows screensavers (that come with Windows initially).
There is a registration key list, where we can see all the registration keys for the installed applications. But this is not that effective, because different programs have various styles in which they store their registration keys (in the registry or in a file, for example).
One thing to note is that if you are planning to uninstall a, for example 30 day trial program and install it again, it is not going to work (for most programs).