In general, autumn landscapes (like the one to the right) and desert scenes do reasonable well. The few Colorado views I've painted haven't sold at all!
It's hard to figure out what collectors might be interested in, so I try to follow the old artist's adage -- just paint what you want, and don't think about the marketplace when you do. That can be a hard bit of advice to follow, but I try!
As a sidenote: it's likely I'll stop placing paintings on eBay and sell them directly from my Website (which just happens to be http://www.southwestspaces.com). I'll need to create a page just for this purpose -- it's on the agenda! Someday. When I have time. (Yeah, right!!!)