Do you mean in terms of ideology/political style, or in terms of their performance in the primaries?
Comparing Lamar Alexander to Rick Perry is just plain disrespectful to Lamar.
The closest parallel I can see is Forbes-Cain in that both are the "rich businessman with no elected office experience and a highly regressive tax reform plan."
I really messed this up. In Lamar Alexanders case, he reminds me of Perry view wise, but is a much better campaigner. In Keyes/Paul, its style and performance. Cain was much better then Forbes (who was as awkward as Romney is) at campaigning.
Santorum has the views of Gary Bauer but has run a campaign that is similar to McCains, while Romney has been this years Bush, as he has been favored from the start.