One question
 

… about presidental elections:

How often has it happened that the loser of a presidental election get to run for president again (not talking about primaries)?

I know that Richard Nixon lost to Kennedy in '60 and ran again and won in '68. But I can't imagine Romney being a candidate in 2016.

pibbur who like his cat is curious

Romney's actually said that he won't be running for 2016. As to the actual question, I can't imagine many - at least not since television and touring across the US have become the norm. Simply too exhausting to the people involved.