Quite a few posts are "What sensor do I use to...?" or Could you explain how Sensor XYZ works?
I ran across this Digikey resource while taking the Design News tutorials.
Digikey Sensors: http://www.digikey.ca/ca/en/techzone/sensors/index.html
Other sites have similar tools -- I just happen to know of this one. I finally gave in and opened an account with them -- not the cheapest but the service is reasonable and the resources are phenomenally good.