Teletubbies

Teletubbies appear/are mentioned in many Simpson's episodes including

AABF07 - Milhouse watches them on TV
AABF07 - Milhouse has Teletubbie underpants
BABF02 - Homer dresses as Tinky Winky to amuse Maggie
BABF11 - They chase Homer with the rest of the PBS mob.
BABF14 - Bart, Lisa, and Maggie watch it at home.
CABF01 - The Family are Telebubbies(except Maggie) in the Couch Gag
DABF10 - Teleboobies name is a parody of Teletubbies
DABF18 - During a sanitized version of The Krusty The Clown Show. Milhouse comments the Teletubbies get away with more then this.
EABF06 - During a Church Sermon at the bowling alley, Dr. Hibbert gets distracted by a plush Dipsy in the claw-grip machine
EABF09 - A plush Po falls out the Simpson's cupboards with various other objects
FABF03 - Teletubbies are at Ruffi's concert.