ALF appears in a police lineup with several other space aliens.
Milhouse sells Bart's soul for ALF pogs.
ALF is mentioned more than once on The Simpsons and has appears in one episode and is referenced in several others.
Season 7, Episode 4 - "Bart Sells His Soul" - Millhouse sells Bart's soul for ALF pogs.
Season 8, Episode 10 - "The Springfield Files" - ALF appears in a police lineup with several other aliens.
Season 10, Episode 9 - "Mayored to the Mob" - ALF appears at the Bi-Mon-Sci-Fi-Con.
Season 34, Episode 13 - "The Many Saints of Springfield" - ALF appears as a walking TV Guide inside Homer's couch during the intro. Known to be the only appearance of ALF with voice acting of Paul Fusco in the series.