Ringtone Maker! Lite

Ringtone Maker Lite lets you create custom ringtones from your iPod library with precise control over the clip start and a fixed 40-second length, plus fade in/out effects.

You can email the finished ringtone and sync it with iTunes. Upgrading to the full version removes ads and adds Manage My Ringtones to save your parameters (start time, length, fade) for quick, repeatable ringtone creation.