The Gallup organization just released a compilation of approval ratings for presidents back to Truman. These are averages of the Gallup data collected on each president during the course of his term rather than a retrospective query of "who was most popular?"

          Approval rating

Truman         45%
Eisenhower    65%
Kennedy       70%
Johnson       55%
Nixon          49%
Ford          47%
Carter         45%
Reagan         53%
Bush I         61%
Clinton       55%

This is taken directly from info on the Gallup website.

Clinton and Johnson more approved than Reagan. Interesting, no?