How can I chop out sections of songs (mp3s) to use as ringtones on my phone?

Is there any particular software I can use to do this? I used to use the sound recorder, but I've somehow completely mucked up my audio settings for recording and I don't know how to fix it lol.
I have got loads of full songs on my phone already, but I wanted to cut certain parts of some songs, e.g. the chorus as the beginning of some songs are really quiet.