Susan Anders has several instructional books and CDs available on her website including The No Scales, Just Songs Vocal Workout,
The No Scales, Just Songs Vocal Workout Volume Two, and  Harmony Singing By Ear. Harmony Singing By Ear is a 3 CD, step by step method for learning how to harmonize above and below a melody.  Both of the Vocal Workouts are vocal warm up and voice training methods that use songs instead of scales to build vocal strength. Susan also has many articles about singing posted on her site.