If your office has an extension system for your phones, try typing up an identical phonelist but just switch all the extensions around. Or if you're tired of your colleague nattering with their mate all day, replace the mates extension with your bosses perhaps? :)

Try supergluing all your colleagues pen caps to the pens and let dry!

Ideally complete the joke by phoning them first thing upon their return to the office and pretend you would like to leave a message for someone...

If your office chairs have a height adjusting lever, try activating it, by taping it to the bottom of the chair. When your colleague arrives it'll be on the highest setting (this works best on taller people as they're most likely to already have it at this setting). Stand back and watch as they sit down and the chair slowly sinks with them!