spotlight: how to exclude html, xml, js files

Spotlight brings up so many files that I don't want (HTML, Javascript, XML, EDML, .class, .properties, .cer) that I have trouble finding the files I do want. I have the following folders checked in the Spotlight "search results" preferences:

Documents

Folders

Images

PDF Documents

Music

Movies

Applications

Is there a way to set the preferences to exclude specific file types by default?