I noticed that Spongebob has made several cameos and parodies in different movies and shows. Here's which ones I know of so far.
Drawn Together: One of the main charactors is a parody of Spongebob.
Alvin and the Chipmunks (Live action movie): The Chipmunks have the TV turned on a few times and each time, 'Spongebob Squarepants' was playing on it.
Daddy Daycare: At the start of the movie, the main charactor's son is getting out of bed and going to the bathroom and he's wearing Spongebob slippers.
The Simpsons: In one episode (I forget the title and season of the episode) at the end, Lisa is praying to Spongebob along with Jesus and some other guy (I forget who).
Jimmy Neutron: I seem to remember reading that in one episode, Spongebob's pineapple made a cameo when Jimmy, Carl and Sheen went scoobadiving.
Fairly Odd Parents: In one episode, Timmy's Dad says "Pants are for squares!" which is likely a joke to Spongebob and in another episode, a guy tells about what he hunts under the sea. He says Crabs, Star Fish and Squirrels.
If there are any other ones that you know of then post them.