From Monday Morning Insight:

Ray Pritchard writes, “In the last 18 months I have come to a few conclusions about how to quickly gauge the health of the churches we visit–either to preach or simply to participate in a worship service. The Lord has allowed us to travel from coast to coast and to visit country cities, city churches and suburban churches–some large, some small, and many in-between. I don’t know if doing this sort of itinerant ministry makes you more qualified to evaluate churches, but the very fact of being in a different church almost every Sunday inevitably forces you to think about where you’ve been, what you’ve seen, and what you’ve experienced.”

I have come to the conclusion that there are two very obvious indicators of church health that the one-time visitor can gauge very quickly:
1. Hearty congregational singing.
2. Obvious affection between the pastor and the congregation.

You can read his whole article here. He also goes on to explain his rationale. HT: Crosswalk.com