If you can code, write yourself a set of scripts that you can configure for different sites.
For example, I have my main file called index.php. It basically contains the barebones html. I then have a config.php file that has everything I need to change from site to site. It has a path variable (I use folders off of a single domain), the image names I use, adsense code, and anything else I might need to configure. My css file is seperate (I'm currently working on a very lightweight template method where I can quickly change themese without rewriting the css file), and the article I want on that site in a .txt file.
All told, it takes me about 2 minutes (tops) to get an entirely new site up and running.
But the trick is to identify the repetative tasks, and make them automatic. Anyplace that you would potentially copy and paste from one site to another, put it in a function and make it configurable. If you can get it so you only have to change code/text in one place, you'll be able to get things moving very quickly.