What are small projects that generate tiny amounts of recurring passive revenue?

What are different techniques for generating tiny amounts of recurring passive revenue?

Bonus points if the techniques is not glamorous or web 2.0. Consider the success of things like Bingo Card Creator. Bonus points if the technique is more about marketing than technology.

Max Klein writes:

I once made a video hosting website
and put 30 ninja videos on it. Adsense
money was about $1 a day. I wrote a
desktop software once, and priced it
at $29.90. I sold one copy a month,
which was terrible. That's $1 a day.
It's really easy as a programmer to do
something that makes $1 a day.

Now comes the trick: If you make 400 things making $1 a day, you will be
making $12.000 a month.

Wow - there are a million things like that - welcome to the soft, seedy white underbelly of the internet!

There is a whole world of what is called affiliate marketing. Do a Google search for it and you'll find that there are companies that will pay you for obtaining a zip code, an email address, getting someone to sign up for a trial offer of something, etc. Big companies are Commission Junction, NeverBlue, and ClickBooth. There are literally hundreds of these.

Now, you need a place to get traffic / potential users / customers. This can range from PPC on Google / Yahoo / Bing, 'review' sites (for example, Netflix compared to Blockbuster, with an opportunity for the person reading the reviews to sign up for a trial of either offer) to YouTube videos with your web site on them, to media buys / banner ads, driving traffic through Craigslist (frowned upon, but done by some) - the list goes on and on.

Time for dinner - if there is interest on this thread I'll respond in more detail later. -e-

EDIT: Note that there are some ways to autocreate sites that do $1 a day (autoblogs with Adsense / banners, etc), but the bar should be higher for anything meaningful. My threshold was $50 / day / site when I was doing a lot of this. I've abandoned this approach to build a 'real' startup, but it is pretty easy for someone to build up a $100/day income leveraging traffic in a relatively targetted way from web 2.0 sites.