Here are some (not all):
Abraham Lincoln and James Madison's highest elective office was congressman. Richard Nixon, Gerald Ford and George H.W. Bush's highest office prior to winning the vice presidency was congressman. Eisenhower held no previous elective office.
I should have qualified that as held a higher office in "modern times" -- nowadays, people are not elected as President when previous highest office was Congressman... but as Lincoln is the only REAL exception to that (others you cited are dealt with below), and his situation was rather unique... well let's go ahead:
GHW Bush failed in seeking the nomination for P and would almost certainly have lost against Carter (Reagan was a Governor and therefore a Washington "outsider" which equals or trumps other choices); when Bush ran in 1988 it was as a sitting Vice President and Reagan's heir (and most would say he was actually elected to serve "Reagan's 3rd term," rather than his own).
Gerald Ford NEVER won an election to be President (nor VP even), he was appointed to both positions.
Nixon, as you cited, was Vice President in a previous administration (under Eisenhower). His election was mainly due to the disarray and disaster of the Democrats after LBJ and the assassination of RFK left them with Humphery (who no one really liked... but he was the sitting VP so the party didn't have much for other choices).
Eisenhower was a successful, touted, publicly famous, and well-respected GENERAL... and THAT seems to trump elected office in the decade or two immediately following a war.
James Madison, while true that his highest
elected office previously had been as Congressman, he was WIDELY known for other things -- mainly as the "Father of the Constitution" (which made him rather unique) -- and he had most recently served as Secretary of State to the Jefferson administration, a significantly public "administrative" office, and was Jefferson's anointed and designated "heir" and by 1808 the Federalist party was way down in "dying" minority status (indeed, The Federalists never won the Presidency after John Adams, who arguable won mainly as a Founding Father, Washington's VP and a kind of 3rd term of Washington -- promising to keep the Washington cabinet intact).
Abraham Lincoln's case was VERY unique in that he won with only 40% of the popular vote -- mainly because his opposition (and indeed the entire country) was so splintered along regional lines (the Dems had "Northern" and "Southern" candidates -- with a fourth party thrown in for good measure) Lincoln just happened to be the candidate from the largest "region" which put him over the top in the electoral college. The regional splits were SO SEVERE, that several states actually seceded BEFORE he took office. Also of note -- at the time he was a Congressman, the House had only 230..231 reps. (BTW, and Lincoln served only one term in the US Congress, while he had been a state assembly man in Illinois back then it was a part-time job... he was known more for his work as a lawyer and an orator than as a Congressman).
So, unless you think Barr has some unique electoral advantage (is the country split along regional lines? If so, does Barr "own" the biggest region?) or perhaps status as one of the founding fathers of the nation, or an important administrative position like Madison (does being a regional Anti-Drug Czar help? Maybe the king of the DOMA?) then... well, his work in Congress as one of 435 people isn't all that impressive or notable, is it?
(Similar limitations were another part of what Ron Paul faced as well, and merely another "justification" for why most of the media never took his candidacy seriously... if he wanted to SERIOUSLY run for President, he needed to have served as a Senator, or preferably a State Governor.)
