The Two Mrs. Nahasapeemapetilons - S9-E7
Trivia: Homer takes Apu to get his hair cut at "Hairy Shearers." Harry Shearer, of course, provides many voices for "The Simpsons."
The Principal and the Pauper - S9-E2
Trivia: Martin Sheen was chosen to voice the "real" Seymour Skinner because the producers had admired his role in Apocalypse Now, and thought his voice would be appropriate for a Vietnam veteran.
Trivia: The musical number "The Garbageman Can" was a nod to musical number "The Candyman Can" in the 1971 classic "Willy Wonka and the Chocolate Factory"