http://mezzacotta.net/garfield - Several different types of Garfield parodies, ranging from variations on the "Garfield Minus Garfield" formula (my favorite of these is "Garfield Divided By Garfield") to haikus to merging or swapping panels/dialogue between two strips to averaging the colors values of each strip to pretty much anything. Warning, though: caused me to procrastinate for two whole days earlier this week until I finally read the whole archive.
http://joshmillard.com/garkov/ - Similar to the Garfield Randomizer, uses Markov chains to create random text out of dialogue from Garfield and then puts this text in emptied text bubbles from a few Garfield strips. I'll post a few strips made with both this and the Garfield Randomizer later. (Can't right now since it's so late.)