How to change default application in OS X

Since I installed xcode, all my ruby files (.rb) opens in xcode by default. I much prefer textmate.

To change the set default application,

1. Select a file on Finder
2. Right click to display the context menu and select "Get Info"
3. In "Open with:" section, you can change the default application.
4. Don't forget "Change All..." to save the change.