In Upside Down and Inside Out: the 1992 Elections and American Politics, James Ceaser and Andrew Busch developed a typology of presidential candidates with two dimensions: liberal-conservative and outside-inside. At the 538 blog, Nate Silver uses something similar to classify potential GOP candidates for 2012.
I might quibble with some of the exact placements. For instance, Gingrich is not nearly as conservative as some think. Nevertheless, the table is a useful starting point.