Edit songs and ringtones with MP3 Editor for the BlackBerry PlayBook
"Use it to create ringtones from a new song you have purchased or to remove unwanted parts from songs or recordings. The touch optimized interface allows you to select parts of the file by swiping the screen and then work with the selection."Of course, if creating your own ringtone is too much work, you can always head over to CrackBerry's free ringtone gallery and download to your heart's content! Just make sure you're logged in to the forums (and if you aren't a member already than what the heck are you waiting for?) and you have instant access to thousands of user submitted ringtones.
More information / purchase MP3 Editor