If you want to get a taste of some of Ray Pritchard's material, check out, this very helpful sermon called "Grumbler's Anonymous." It was preached a couple of weeks ago at the graduation ceremony at New Brunswick Bible Institute. It describes the trap that many people in ministry (and in the secular work force) fall into which involves comparing ourselves to others and getting discouraged (and grumbling). A very helpful biblical exhortation (based on Matthew 20:1-16) to serve faithfully and not compare ourselves to others.
There are a lot of other good resources available at Keep Believing website as well.