WHEN I WAS IN the military, the installation rabbi was normally the first religious visitor to call around to welcome me to the neighbourhood. He was keying off my name "Bernard Goldbach" ("That's a very good Jewish name, isn't it Marvin?") and ignoring his paper clues that identified me as Catholic-ish. Now there's an excellent online resource that explains everything Jewish.
Wikipedia -- Jew
Justin Mason -- "Googlebombing in a good cause"
Bernie Goldbach curates genealogy links.