Guided Lovingkindness Meditation
This is an example of a guided Lovingkindness meditation put out by University of New Hampshire Health Services. In contrast to other meditation techniques, there is a lot of room for ad-lib in these guided meditations and even the same teacher will probably create new scripts for each session.
Guided Metta Meditation
Another guided metta meditation, this time from a yogi. There is a lot of crossover in these practices between Buddhist teachers and the yogic tradition.
Bhante Vimalaramsi Explains Lovingkindness Meditation
This is an extended talk from Bhante Vimalaramsi at the beginning of a "Lovingkindness Retreat." He describes metta meditation starting at 2:06.
Guided Lovingkindness: Michael Sealey
One more example of a guided Lovingkindness meditation, perhaps the most relaxing metta on the web. Don't listen while driving! The relaxation portion lasts until about 7:00; he gets into a version of Lovingkindness from there. You can see how diverse these guided meditations can be.