A great source for information about The Simpsons is a site called Springfield Nuclear Power Plant. I don’t know why the designers chose that name, but it boasts one of the most comprehensive collection of episode guides to the show on the Web. Early seasons have episode guides that are dizzying in their breadth and depth. Later seasons have briefer guides that are still better than nothing.
If you’ve got The Simpsons Season 1 and Season 2 on DVD, this site makes a great companion to demystifying the dozens of allusions and references each episode contains.