Where can I find a resource that will let me look up the name of something (mostly mechanical) and find out which supplement it came from? I don't need stats or anything else that is restricted, just a place to start looking.
I'm thinking an article in the resource would read something like:
First appearence: PhB
Subsequent appearences: Splat book 2B, Dragon magazine X-Y
Does something like this exist? Bonus points if it's free.