A lot of writers that spend their days on Web content eventually seek out some residual income for the weeks when gigs are scarce. Aside from selling ebooks and seeing the sales trickle in over time, there are a number of sites that can supply you with a small residual income. All of these sites pay small amounts based on how popular your content is, i.e., how many pageviews and clicks you get. This can be simply from the number of people who look at your content, or it may be AdSense revenue.
Triond- This is a revenue-share site, which bases its payments on the amount of revenue your articles bring in for the site. After you upload your file (one file per article), the site approves it and it's set up on one of their many content sites. You can track your pageviews and income per article on the main site. In addition to articles, it also accepts poetry, essays and pretty much anything that people may be inclined to look at.
Squidoo- Squidoo is a place where members create "lenses," which are just easy-to-build web pages. Some people use them to promote their services, some use them as writing samples, and some use them for affiliate sales. You can also combine their uses and stick some affilaite links on a lens that promotes your writing services while providing writing clips. In addition to the affiliate sales that are possible, you also earn a small amount on your lens, depending on how popular it is. Even if it gets very little traffic, you earn a very small amount each month, and it's payable via PayPal.
HubPages- The income from this one is based on your own AdSense income. You approve the site to be added to your AdSense account and you keep any income that comes from it. Each HubPage is a separate Web page, kind of like a Squidoo lens. There's no limit to how many you can make. I've heard that making 50 or more can bring in a nice residual income every month. Of course, it has to be something that people want to read in order to start raking it in.
eHow- Writing articles at eHow isn't too terribly taxing, but again, it has to be something that people want to read. There are people that do very well there, and there are people who make pennies or less per article. The only payment is from some proprietary formula based on, something or other. They won't actually say what it is, but I'm assuming it's based on the amount of income the article generates. eHow has a very specific format for their articles, but once you get that down they go much more quickly.
AC- The old standby, Associated Content, started paying residuals last year. Fortunately, that means that the people who were paid for the articles they wrote for the site before the residuals started are being paid extra for articles that were already paid for. Unfortunately, it means they pay much less, or not at all, for most of the new articles that come in, hoping that residuals are enough to keep people writing. And, so far it has been. To keep the residuals coming in, you have to be active on the account at least every 90 days. The amounts are based purely on your pageviews, though they sometimes offer an upfront payment as well.
Suite101- This one pays based on pageviews, but it has a good readership and a high placement in the search engines. I have roughly as many articles here as I do on Triond, but my residuals are three times higher on Suite101. The residuals go on as long as the articles are on the site, even if you stop writing for them.
Helium- There are residuals, but they are supposedly the lowest available pretty much anywhere. I've never written for them, and there may be someone somewhere who does well for them, but I've only ever heard of writers who ended up making little to nothing and regretting their time spent on Helium content.
How to Do Things- This site is another AdSense revenue site. The readership is medium sized, so there is some potential there. My articles were put up back when they paid for them, so I don't know how much the AdSense brings in. I do know, however, that my articles there have averaged more than 1300 views apiece, so articles on lucrative topics have potential.
Residuals may not pay much in the beginning, but the key is really to build up the volume of them. On most of these sites, whenever you post a new item, the views for the other items go up as well. This of course means that people who read your stuff will want to read the other stuff you wrote. Keeping some fresh content going in keeps views and revenues steady. I don't know that anyone could live off Web residuals, but they are nice to have during those slow times.