Not many replies this time around, which is too bad since I love reading these threads. There are links to the previous posts in there.
I usually talk about the same projects of mine, so this time I'll talk about a few smaller projects instead that also make money on the side.
http://www.daterangepicker.com -- a JavaScript widget for choosing date ranges, like hotel reservations or dates for a report. Initially it was just a post on my blog and a zip file. It got so much traffic I put it up on Github and gave the thing its own site. That site gets over 1000 daily uniques. I put one small banner ad in the sidebar, and that generates $200-400 per month.
http://www.websitegoodies.com -- A site I started in the mid-1990s to share what I learned as I taught myself web design. All the articles and tutorials became outdated, but the tools still had some popularity, so I rebuilt the site around them one weekend. A banner ad or two on each page generates $50-100 per month.
I have a few very old sites that resell another company's advertising services. Almost all the customers are new site owners, small businesses, that sort of thing. After checkout, there's a "resources" page in the customer area of the site with links to SEO services, payment processing services, and other things a new site owner might need. Those are all referral links, and I earn $200-300 per month in commissions for the business those links generate.