Almost President: The Men Who Lost the Race but Changed the Nation by Scott Farriss
Apparently the reason we have had very little trouble with the losing candidates and their supporters rioting in the streets is all about the concession speech. The winner isn't a winner until the loser conceded that the other guy did win. Huh. Interesting.
This book doesn't delve into every losing candidate but does hit on several interesting ones who had important careers both before and after losing the presidency to someone else.
If you have any interest in those other guys, read this book. It's worth it, and a very readable look into a past we soon forget about. And if you want a whole list of also-rans, check out this bank in Kansas!