I love Martina McBride’s “Whatever You Say”
I also like Pam Tillis’ “Shake the Sugar Tree”
Tim McGraw’s “Indian Outlaw” and “Live Like You Were Dying”
Garth Brook’s “The Night I Called The Old Man Out”, “That Summer”, “The Dance”
Big N Rich - “Save A Horse Ride A Cowboy”
Brooks and Dunn - “My Maria”
I like all of these and not all of them are necessarily hits, but they are pretty good, IMO. 
Now I’ve got a list of CDs to get. Thanks, folks! Especially folks who recommended Johnny Cash, Emmy Lou Harris, and Willy Nelson along with others: when you pair up recommendations for folks I don’t know with recommendations for my favorites, that’s a great sign I’ll like the new folks.
One more recommendation. Check out Robert Earl Keen if you haven’t already. He’s fantastic. His shows are always a mix of hipsters and shitkickers, and his music is just wonderful.
Daniel
Check out Jimmie Dale Gilmore (with or without The Flatlanders) if you like heartfelt twang, and BR549 if you like a bit of rock with your country.
I’m not sure if he’s even still recording, but I think Ricky Van Shelton has the prettiest voice in country music.
Sorry–I forgot that this does tend to happen!
I LOVE Robert Earl Keen! And if anyone would like to take a listen to the alt-country / Americana end of the spectrum (to which REK belongs), I highly recommend This Is Americana and This Is Americana, Vol. 2. These terrific full-length CDs are great introductions to this sub-genre, and because they are fund-raiser CDs to support Americana artists, all the proceeds go to that end and the CDs cost less that $2.00 each. So if you don’t like the CD, you’re out 2 bucks.
That’s kind of a trick question. I don’t love Tuvan throat singing or Bolivian funeral dirges, but they’re not essential parts of my culture. Americans who look down their nose at country music are, for the most part, unaware of how country has influenced music that they do like, or how similar some of it is to music they profess to enjoy.
I’m not particularly knowledgeable about opera or Hip Hop, but if someone whose opinion I respect recommends a particular side, I’ll at least listen to it once. I listened to Nusrat Fateh Ali Khan on my auto mechanic’s advice once.
I saw Robert Earl Keen a few months ago at the Birchmere down here. The show was incredible. I cannot believe I forgot to recommend him. Country live is just so much fun, especially in the smaller venues.
featherlou, if you’re compiling an “old country” album for your mom, you simply MUST include “Who’s Gonna Fill Their Shoes” by George Jones. Might not be a bad idea to include George Strait and Alan Jackson doing a duet on “Murder Down on Music Row”
I can’t imagine an old country mix w/out using something from The Nitty Gritty Dirt Band: Will the Circle Be Unbroken Vol’s I, II, & III. I think they are awesome, w/ II being my personal favorite. 
I’m probably the most unpatriotic person evah and can’t stand rah-rah-USA songs, but it’s a tribute to his writing skills (he had success as a writer for quite a while before recording himself)and his delivery that this one makes me tear up. He talks about opportunity but not in an over the top way, or to the exclusion or beat-down of other countries.
I have to disagree with Martina McBride “In My Daughter’s Eyes”, “Concrete Angel” and “God’s Will”. I loved “My Baby Loves Me” and the bordering-on-glurge “Independence Day” and even “Broken Wings”, but she goes off the deep end of the glurge pool with those first three. They’re barely country anymore, and more easy listening.
I must hijack this thread to note that Joe Nichols (Tequila Makes Her Clothes Fall Off) was chosen to and is singing at Anna Nicole Smith’s funeral in the Bahamas. Definitely falls under the “you can’t make this stuff up” category 
VCNJ~
But is he singing “Tequila Makes Her Clothes Fall Off”? That’s the question.
As long as we’re making recommendations, let me suggest Lucinda Williams. Not strictly country by any means, but also with elements of pop, folk and blues. She writes incredible songs, sometimes complex, sometimes cutting right to the bone. And oh, that voice. You’ve never heard such an expressive voice. If you could make love to a voice, this is the one you would want. I don’t know how to put it any other way. I suggest “Car Wheels on a Gravel Road”. Yes, this album got an incredible amount of hype and critical acclaim, and even won the dreaded Grammy for Best Contemporary Folk Album. But in this case, you can’t afford to not believe the hype. You have no reason to trust me, but please trust me!
A good country station on the net is Boot Liquor which is currently hosted by the good people at www.somafm.com