I'm in the same boat as Sabre. I start about 1 new mini-site per quarter, dealing with a different small niche.
I try to find someone who has built up something strong - tons of content and passion - but no idea what they're doing! I wait till they've given up and buy those. Then I work on the link building, promotion and keeping them active. These pay for themselves and make extra money each month to add to my pockets, nothing too exciting though.
Most of my income comes from one big site that I put most of my effort into. The purpose of the various small sites is to be diverse in the event of a change in traffic or the fallout of a revenue model.
One avenue I have found surprising success in has been free Web 2.0 profiles that allow me to create a blog, diary or the like, without having to host or update a domain name. I start a few a month based on Amazon products I like or experiences I have had that might help others. Some only have a couple of pages, others have more than 20. These actually are starting to make consistent money, more than enough to offset my costs on the other projects.