Registry Commander is a Free Alternative Registry Editor created by Anders Jakobsen. It can be used as a replacement to the default Windows Registry Editor, RegEdit.
MJ Registry Watcher is a Portable Registry Montioring Tool that can monitor your system registry and then prompt you regarding any changes made to registry keys files or folders. Once running, the tool minimizes itself to the taskbar.
Regshot is a tiny open source portable registry comparison tool. It allows a user to take a snapshot of the system registry and compare any registry modifications made after doing system changes or installing new software.
RegASSASSIN is a portable registry tool that can be used to remove even the most stubborn of registry key entries. It does this by resetting any of the key's permissions and then proceeds to delete the entry.