Alternative to Your Own Blog
The inclination for most people upon hearing about the earnings potential of a successful blog is to start one of their own. This makes sense since owning your own website provides you with the most flexibility when it comes to controlling the design and content. Creating sites is what I've done in the past and what I'll likely continue to do in the future. But it's not the only way to monetize your writing.
The alternative to creating your own blog is to join an existing content network such as About.com. Most networks are small and there is always the chance that they'll fold from a lack of funds, but About.com has proven to be a stable and long-lived site. Their pay-for-content program at one point guaranteed you $725 per month as long as you qualify and meet their minimum posting requirements. And apparently successful authors are able to clear $100,000 a year. That's pretty impressive considering you need nothing more than a computer and an Internet connection to get started.
Additional advantages include being able to piggy-back off of the success of a well-established site. This means associating yourself with a domain that Google and other search engines trust as well as being immediately "hooked" in to the site via cross-links that About.com (likely) generates automatically.
The disadvantages are, unfortunately, numerous, but likely worth overcoming giving the potential earnings. First and foremost is the trouble finding an available topic that you have some expertise and/or interest in. More likely than not the current list won't contain anything of interest so you'll need to monitor existing categories for openings when the current author moves on. The last time I checked, this was the link for finding categories without authors. Be warned that there is an approval process for new writers including which at the time of this writing included a 4-week training period.
While the idea of joining About.com seems like a good one to me, I can't help but think that I'd be leaving money on the table. I have to assume that About.com is paying out no more than 50% of the ad revenue which means that your content is earning them $1500 a month. If you could attract the same traffic levels on your own site you could double your revenue and maintain complete creative freedom. Of course, attracting a good amount of traffic is where most people fail.