Definitive albums?

I've been decently familiar with the Genesis body of work for a while, but haven't been able to get into the albums individually - probably because I made the mistake of trying to force myself to start at the beginning and work my way through. That got me burned out quick. So, what would you say are the definitive albums - one from the Gabriel era and one post-Gabriel? Where should I begin?

Edit: Thanks so much for all the great suggestions! The most popular by far have been Selling England, Trick of the Tail, and Duke, so that's where I'll begin.