[Cypress Knee]

Mike Cross has written some good ones. They can be found on an album called Mike Cross: The Best of the Funny Stuff. One example - Elma Turn. Here is the opening line:
"Elma Turl is a beautiful girl, and I'd love to have her for my wife,
She's just the kind of woman who could make me happy for the rest of my life
My daddy said, "Son, there's something you don't know, and it's something I
think you oughter
Elma Turl is a beautiful girl; but son, she's my daughter."

If anyone is listening, the killer punch line is at the end of the song.

Antsy McClain and the Trailer Park Troubadours have some amusing material too, such as "I Married Up" and "Prozac Made Me Stay".

"She's in her brown fuzzy slippers and a mustard yellow Terry Clothier robe
She's got her mail-order Richard Petty earrings dangling from each lobe
She's got her hair up in rollers and the rollers are mountain dew cans
She's a picture of grace with that grilled spam n' cheese in her hands"

etc...

"I married up...."