A small single-page info-site I made in a day or two some time ago started picking up traffic and now makes around $500/month from adsense ads. Quite nice for the work put into it, but of course if you take into account all my sites and apps that made nothing it's not much for the total effort. But now that it's getting traffic I have some ideas for building it out into a larger site, but I haven't found the time yet.