Geek Brain Teasers

muce writes "A few days ago my cube mate entertained a lot of us engineers by presenting us with the famous Monty Hall problem. That problem sparked a day of strong debates, coding simulations, and ramped writing of equations on whiteboards. Since then we've been thirsting for more good geeky mathematical brain teasers to pass the time at work. Does anybody know of any good ones like the Monty Hall problem, or by chance is there a web page with a collection of them?"