Andreas Viklund has 11 free CSS templates. The designs are clean and smart, and are probably pretty friendly to modifications. Andreas says the following about the templates:
These are my free XHTML/CSS website templates. They are free to use for any purpose without any limitations or obligations. I kindly ask you to keep the small credit link (the line that says “Design by Andreas Viklund”) since it is a nice way of giving something back to me. But that is only a request, not an obligation.