The Free MP3 Cutter is a great application for cutting and joining music or audio files to make your own toque do iphone. It also allows you to choose a starting and ending point for the output file. You can also save the selected ringtone as a separate file and send it to your phone. It supports most types of phones.
The best ringtones for mobile will be able to play to any audible range, so you won't have to worry about listening to the same tune over and over again.