I lied, one more! O Bury Me Not On The Lone Praire, which I first heard by Cash. Just now heard it again on the soundtrack to She Wore A Yellow Ribbon, which I’m currently watching.
If I could choose only one, it’d be George Strait’s Amarillo by Morning.
Others that are way up there include:
[ul]
[li]Willie and Merle’s version of Pancho and Lefty (songwriter Townes Van Zandt makes a couple of appearances in the video)[/li][li]Gene Watson’s Got No Reason Now for Going Home[/li][li]Larry Gatlin and the Gatlin Brothers’ What Are We Doin’ Lonesome[/li][li]Alabama’s Old Flame[/li][/ul]
Here’s a link to **Wheelz’ **You’re the Reason God Made Oklahoma, which is one of my favorites, too.
I’m a big fan of Patsy Cline and Hank Williams, too – but the songs listed above come to mind first when answering the OP.
Rodney Crowell – I Couldn’t Leave You If I Tried always makes me smile.
George Strait – The Cowboy Rides Away makes me cry.
Ricky Van Shelton – I’ll Leave This World Loving You always amazes me with the quality of his voice.
Patsy Cline – Faded Love – 'nuff said.
But if I had to pick just one, it’d probably be Marty Robbins – Don’t Worry.
Actually, anything by those five singers, or anything by Johnny Cash. And Dwight Yoakam. And BR 549.
Dammit!
Steophan’s mention of Long Black Veil reminded me of another one: Roseanne Cash’s version of Sea of Heartbreak, which many, including her father, have sung, but I like her version (which includes The Boss on backing vocals) the best.
If you’ve not heard the rest of Roseanne’s 2009 album The List, I highly recommend it (it’s got her version of *Long Black Veil *on it, too). I think she’s a criminally underappreciated artist.
Just read AuntiePam’s response; dammit, indeed! Forgot all about Dwight. Ain’t That Lonely Yet is probably my favorite of his, but that’s another list all by its own self.
If I said you have a beautiful body would you hold it against me
I Love the Bellamy Brothers.
Seconded!
And after traveling 600 miles (twice) to see him, I forgot all about Jimmie Dale Gilmore!
I can’t choose. I love 95% songs in this thread, and the ones I don’t love, it’s just because I don’t recognize the titles. But other songs I’ll add to the list. (As they come to my mind with no real order)
- Tennessee Waltz*
Big John
Guitars and Cadillacs
Blue Moon of Kentucky
Friends in Low Places
The Dance
King of the Road
Mamas Don’t Let Your Babies Grow Up to be Cowboys
My Heroes Have Always Been Cowboys
Mama Tried
I shall have to check out that Rosanne Cash album, her song September When It Comes, a duet with her father in one of his last performances, is beautiful.
Another recent album worth mentioning is All I Intended To Be by Emmylou Harris from a couple of years ago. One of her best, I’ve listened to it countless times since it came out.
Something about the things you said here made me want to try to locate a Ricky Skaggs a capella version of an old gospel song that (to me anyway) is as close to a musically perfect voice as I have heard. Unfortunately Ricky’s version isn’t on YouTube at the moment, but I did find this a capella version that blew me away. I have to share it. First time I’ve heard of this singer, too! It won’t be the last.
Ah I meant to mention this song! Any song with the lyric “I turned twenty-one in prison doing life without parole” has to be up there. It gets my award for Most Country Lyric Ever, too 
Lyle Lovett – Nobody Knows Me
What’s your mama’s name is my favorite female country song
that little green eyed girl line is soooo good.
I’m gonna go with Cigareets, Whusky, and Wild Wild Women.
I don’t think I could pick just one. There’s just way too many good ones.
Actually, if I had to pick one, it would probably be Hank Jr’s Family Tradition. Maybe not the best song ever but singing along to it is fun.
I let iTunes makes the call. It’s the Louvin Brothers’ version of “In the Pines,” which edged out “Angel Band” by the Stanley Brothers.
I don’t know, I kind of want to take back what I said and choose a song from either Hank Williams or Patsy Cline.
Can’t believe you’re making me pick one song. 
There can’t be just one, of course, but here are three that are worthy:
Four in the Morning, by Faron Young.
Seven Year Ache, by Rosanne Cash.
Honky Tonk Heroes, by Waylon Jennings.
He was in New Grass Revival with Sam Bush, Bela Fleck, and Pat Flynn. Amazing singer, extraordinary mandolinist, THE banjo player, and excellent under-recognized guitarist all playing together – just WOW! Here they are doing Holly Dunn’s “Love Someone Like Me.”
Very nice! Thanks. I’m familiar with Bela and Sam already, but I guess I haven’t been keeping up too much with their work. Cowan is special, no doubt.