Great list! Here are some more:
Sunday Morning Coming Down - Johnny Cash
Beaches of Cheyenne - Garth Brooks
Tequila Town - Brooks & Dunn
Walking After Midnight - Patsy Cline
My Son Calls Another Man Daddy - Hank Williams, Sr.
Okie from Muskogee - Merle Haggard
He Stopped Loving Her Today - George Jones
Weed with Willie - Toby Keith
You Can't Make a Heart Love Somebody - George Strait
While Johnny's voice and phrasing are a huge part of what makes 'Sunday Morning Comin' Down' worthy of this list, it is worth noting that the tune was penned by Kris Kristofferson - who was cruelly cursed with an inability to decently sing any of the wonderful songs he wrote.