Interesting question, Jason. Here's an excerpt from a related item from allmusic.com:

The Last Thing on My Mind" dwarfed that success, however. A song of regret over the loss of a relationship possessing some of the emotional distancing of Bob Dylan's "Don't Think Twice, It's All Right" (though none of that song's bellicosity) and the later hit "Always on My Mind," it finds a lover telling his departing companion that "I could have loved you better, didn't mean to be unkind/You know that was the last thing on my mind." It quickly became a standard. In 1965 alone, covers appeared on chart albums by the Mitchell Trio, Peter, Paul & Mary (another Milt Okun act), and Marianne Faithfull. After that, "The Last Thing on My Mind" spread to country artists, earning recordings by Charley Pride and Hank Locklin in 1967 before the duo of Porter Wagoner and Dolly Parton released it as a single that peaked at number seven in the country charts in early 1968. Rock acts such as the Move and the Vejtables tried their hands before Neil Diamond put it on his 1971 MCA album Stones, and after Diamond left MCA in 1973, the label belated released it as a single that peaked at number 56 on the pop chart. The list of other artists who have recorded "The Last Thing on My Mind" includes Bill Anderson, Chet Atkins, Joan Baez, Harry Belafonte, Glen Campbell, Judy Collins, Sandy Denny, José Feliciano, Flatt & Scruggs, Anne Murray, Willie Nelson, the Seekers, and Hank Snow.

So, that's a start.
-Joe-