First, a Web service that "meets an unmet need." Back in 2005 I built a "code snippets" site using the then-nascent Rails in just over 24 hours. I then spent a second day making the design more "Web 2.0" a few months later, but otherwise did little except mention it here and there and add my own code into it. It made ~$800 a month from Adsense for a couple of years and then I sold it to DZone for $30,000. Perhaps the lowest time vs money work I ever did.

Second, sell a killer screencast or e-book. You'd need to actually be good at making one of these, of course, and have a very good presentation. If you have domain specific knowledge, though, you may have something valuable.