John Tyler also served in the Provisional Confederate Congress and was elected to the Confederate House of Representatives, but died before taking up the latter post. Andrew Johnson served briefly in the U.S. Senate after leaving the White House.
Since Q, ex-presidents seem to have taken the attitude that they have done their duty and are entitled to a quiet retirement. Another exception was one-term president Taft, but he had always wanted to be on the Supreme Court. Obama has been unusually active, but he obviously thinks the situation is desperate and still I can’t see him pursuing any elective office.