Ok, this one is for the serious nerds only. Competitive Programing is a rather entertaining thing to in your free time that can even earn you some money. Here is what you do, you go down to topcoder.com and register for a free account. Then you have a few options, you can compete in their Algorithm competitions, which are timed programing exercises. Or you can compete in their software design or development competitions, in which you not surprisingly develop and design software. The best part about topcoder is that the winner gets paid so it is not only fun but profitable.