I don't know of a free one but I used audiocleaner to manage MP3s. Initially I bought it because it converted all my magnetic tape and vinyls to MP3 format and cleaned up the hissing noise and crackle effects. But then I found you can splice and merge existing MP3s with it and yeah like you I used it to cut out intros or outros. Or even to make melledys of several tunes into a ringtone

It's easy to use and not that expensive.

http://www.nextgenelectronics.com/magix.shtml