I guess it all depends on what you mean by "under-rated." "Coming Up" wasn't, it was a smash hit. "1985" I suppose could be included, an absolutely top Macca album track, and add "Mrs. Vanderbilt" if you are going that way. I think "My Ever Present Past" is a fab song that belongs there, and let's include "My Valentine," "Let Me Roll It," "Junior's Farm," "Take it Away," "Ballroom Dancing," "Wild Life" and "Biker Like an Icon." These are all fine songs fans know are great, but that get almost no attention from anyone else, and some get occasional sneers for no reason.
Oh, is that ten already? Easy list to make.
For honorable mention, I would include:
"Ebony and Ivory" - yes, a smash hit, but gets way too many sneers these days, it is what it is, a beautiful reflection
"Come and Get It" - how often do you ever hear this associated with Paul?
"Monkberry Moon Delight" - I think fans appreciate this tremendously, general public never heard of it
"Mamunia" - beautiful song nobody has heard of
"Silly Love Songs" - yes, a signature song and hit, but it is fashionable for fans to find fault with a brilliant song, which mystifies me
"Those Were the Days" - Paul didn't just sing, play multiple instruments and write - he also produced beautiful songs like this for others
"Goodbye" - kept off the top of the charts only by "Get Back," so for all intents and purposes a Macca #1 few even know was his.