I don't know if this counts as your typical work-from-home situation, as it still is similar to finding an opening and being hired at a job in the regular work place (unlike places like ChaCha or surveys, where most anyone can join). But I do work from home, so I'll share it anyway.
I do copywriting for an SEO (search engine optimization) company. I am assigned a client(s) for whom I write blogs/articles -- not publicity-type things, but 400-600 word articles that speak to their industry and include certain keywords. I then syndicate/bookmark those articles online to help their rankings. It's not rocket science, but does require a decent writing ability (hmmm...not that all SEO companies are so picky about writing ability, accuracy, or even the basics of spelling, however, judging by some that I've read) and sometimes a lot of creativity to come up with topics. For instance, I had a residential window tinting client. After so many months the ideas on window tint were stretching veeeery thin
I do everything online, including communicate with my "employer". I do have to pay my own taxes as I am considered an independent contractor. Clients come and go, so it's not steady enough for me to rely on a certain income. In other words, I would never take on an expense supported by this salary, like a new car payment or increased mortgage. But it's nice for work-from-home, "extra" money -- we use it to increase our savings.
Also, I can't honestly say how easy or hard it is to find this sort of job. I was lucky in that I had a friend whose sister owned a small SEO company. I imagine you could just search online for SEO companies and submit an application. I don't know what those other companies require in their copywriters, but I was hired in part for my BA in English.
Hope that helps someone!