- http://www.tweepsect.com/ - Gets 300,000~600,000 pageviews per month (about 1/6 uniques), makes a couple hundred bucks from ads each month. Been around for almost 5 years.
- http://colorblendy.com/ - There's also a Chrome app (20k weekly users), website gets about 4,000~8,000 visits/month. I had some ideas for making a "Pro" edition with things like importing/exporting colors from/to CSS stylesheets. Probably need to do some more market research before diving into this.
- http://wedomainsearch.com/ - Few hundred visits per month, brand new (built several months ago). Fairly cool idea that is really valuable for founders/hobbyists, I use it all the time. Needs some love for promotion and monetization, though.
I love working on these little stand-alone projects (a few more here: http://shazow.net/, also my email address if you want to reach out), sometimes I wish I could just whip them out and sell them as a living but the code alone is never as valuable without putting in effort into growing the audience.