I just received an iPad for Christmas from my wife. She is very non-technical and did not know exactly what model she bought, so I had the same question: do I have a retina display?
As best I can tell, only the new 4th gen models have the retina display, and only the new 4th gen models have the smaller new "Lightening" connector instead of the older, wide 30-pin connector.
So, knowing if you have a retina display seems to be as easy as looking at your iPad's connector. If 30-pin, you do not have retina display. If Lightening connector, you do have retina.