[rover]

It's pretty simple and managed by OSX.

- Select a filetype you'd want to change the default application for and open the File Info (Cmd+I) - In the "Open with" section, select the app you want to be the default app for the filetype - To persist the default app along the whole filetype, also click the "Change All" button right below it.

[Watabou]

You can also hold down the open button and a list of alternate applications that can be used to open the document drops down. Pretty handy.