Unassoc

If you're looking for a quick way to remove file associations for a specific file format on your computer, one of the easiest way to do the job is to use Unassoc.
This application has been developed to serve a single purpose, so the design is pretty basic. Of course, everything's very easy to use, as all the features are grouped in the main window for quick access.
And speaking of the main window, it's a minimal screen that displays all file types on your computer, alongside the dedicated tools to remove file associations, delete file type and refresh list.
Additionally, the application also sports a separate search tool that allows you to search for a certain file extension quickly.
Of course, the file association removal process takes just a few seconds, as you're only required to click on the desired file format and hit the “Remove file association” button in the main window.
The application is far from being a resource hog and it remains very friendly with computer resources all the time. Still, keep in mind that it only works on Windows Vista and 7, with administrator privileges mandatory to make modifications to file formats.
Overall, Unassoc is a handy tool that does what it says without assaulting the user with any other unnecessary features.
It sports just a minimal window, a long list of file formats and the basic utilities to serve its purpose in a quick manner. Of course, there is no help file included in the package, but chances are that you don't even need one since everything's so easy to use.