In honor of the impending 500th episode of The Simpsons, former writer/showrunner (and current Portlandia writer/producer) Bill Oakley just tweeted the "top 10 episodes that were pitched, discussed, written but not aired." It's the best possible thought experiment: imagining just what these episodes would have been like had they been produced around season 7 of the show. I mean, come on, "Bart Gets 144 Jeeps"? "Prince Comes to Springfield" by Conan O'Brien?! Good god. And hey, it's not too late! Maybe one of these can become episode 513 or something.
And if you missed Oakley's contributions to this here website, which include a peek at how the early era [...]
Below is the final outline for "Sweet Seymour Skinner's Baadasssss Song", by Bill Oakley and Josh Weinstein. This was the 18th episode of the fifth season and the 100th episode overall of The Simpsons.
This document is a part of The Lost Jokes and Story Arcs of "Sweet Seymour Skinner's Baadasssss Song", a feature that has co-writer Bill Oakley running through the writing process for this episode and all of the jokes and story arcs that had to be cut. He also goes over the general writing process The Simpsons from seasons 3-9 and where the first draft script fits into it.
Also be sure to check [...]

Ned Flanders writes a Christian sci-fi book. Grampa Simpson visits the set of Matlock. Jimbo finally graduates from Springfield Elementary, leaving Bart all of his troublemaking supplies.
These are ideas for early Simpsons episodes by former showrunners Bill Oakley and Josh Weinstein from a document they recently unearthed from an old hard drive. "Unused Stories and Premises" is an incredible look at the writing process from the golden years of the show, one that shows how tiny jokes were turned into classic episodes.