I used to dabble with websites and I would put ads for this one dating site on my websites.

I would make these goofy greeting card things that ppl could send to other ppl....viral marketing at its best.

Every greeting card that got sent had my ads on it at the top or bottom.

I made a few grand doing that. Every month, the dating site would send me checks for the traffic I sent them...in US$.

About 2% of my visitors would click on an ad. Each click would pay me 5-10 cents each. If the person signed up for the free membership, I would get another dollar. If they signed up with a credit card, I would get 50% of the sale.

I gave it all up when I decided to go and live on my sailboat for a few years. Now that I'm landlocked again with a steady internet connection, I might get back into it. But it wil be harder as there is way more competition for your clicks now.