There's also Hobbes and Bacon, a fan-drawn series that picks up with adult Calvin (now married to Susie) giving his old Hobbes toy to his daughter. Very well done and nostalgia-inducing.

Part 1: http://www.pantsareoverrated.com/archive/2011/05/10/hobbes-a...

Part 2: http://www.pantsareoverrated.com/archive/2011/05/12/hobbes-a...

Part 3: http://www.pantsareoverrated.com/archive/2011/10/11/hobbes-a...

Part 4: http://www.pantsareoverrated.com/archive/2011/10/13/hobbes-a...