One oft-mentioned method of generating money is taking advantage of affiliate programs of various sites. Problogger and other sites championed this method of earning revenue, but it can be hard to decide what product you’d like to promote. I’ve found it most useful to find something that is popular but not entirely saturated.
Let’s say, for example, you want to make money by promoting dating sites. While the market for dating sites is pretty well saturated, there are affiliate programs for niche dating sites as well. Being a dating affiliate could allow you tap into a very broad market, if you could bring in the traffic and properly direct them to the programs.
As always, do your research and decide what product promotion would work best for you. There are tons of available opportunities, the real difficulty is pulling in traffic and converting it.