Looking to make money on the internet?

This was one of the furthest things from my mind a few weeks ago, until a co-worker told me about his website.
I brought up the subject and was surprised when he told me about it. He said he made $1800 in the month of January 2009, his best month yet. The other months he made around $200 to $600.
He told me could have done better if he had spent more time developing his ads.
Not bad money for what little he has invested and the amount of time he spent on it.