Homer Simpson's version of Do-Re-Me was recently posted in another thread.
One reason Lewis Carrol's Alice books were popular was that many of his poems were parodies of stuffy poems the kids had to learn - see The Annotated Alice version for details.
I liked the Millenium Pie parody of American Pie last year.
And Miles Kington (or was it Alan Coren?) has a great story about Lewis Carrol trying to publish "The Jaberwocky" but there wasn't time to proof read it, which is why it is like it is.
I will try to find references to these and dredge a few more from my memory and post them later.

Ro* Ward