One of the best sites I've ran across lately is Garfield Minus Garfield. Just like the name implies, it's the same Garfield comics, except Garfield has been removed. As the site notes, the result is "a journey deep into the mind of an isolated young everyman as he fights a losing battle against loneliness and depression in a quiet American suburb." It's a little suprising how taking out a character gives the strip a very different feel. Can you think of any other strips this might work with? Maybe "Calvin Minus Hobbes"?