Professional house sitter. I read about a retired couple who got paid to stage luxury homes for sale. They garden, keep the place clean, and live in million dollar homes. A friend of mine did some of this after a divorce, but she found that she had lots of choices from April to August, not so much September to March.
+1. In seasonal vacation locations* there are alwasy a large percentage of homes that sit vacant for 9+ months out of the year. Like axecleaver said, you stay there and do odd jobs and generally keep an eye on the place while the owners are away. The downside is that you loose your housing when the owners want to come back (sometimes with little/no warning), it has to be kept in a perpetual state of tidiness and you can never personalize it to your tastes. I've had a few friends who have done this for several years - when they get displaced by the owners they travel and couch-surf.
I've also read about people who live in homes that are 'staged' (furnished to sell) for sale, particularly in markets where homes might sit for a couple of months before being sold. Similar deal, only here you have to be super clean and you often have only a few hours to get you and your suitcase out so the home can be shown to someone else.
*as examples: Coastal Maine, any beach town (during the winter), near any ski resort (during the summer), around lakes, etc.
