I have to dissagree with Toby Keith. I think he sounds like a big ol' billy Goat! I mean, what's with that dramatic machine gun vibrato he's picked up in recent years??
Garth is possibly the greatest entertainer that country music has ever known, but as far as vocal talent, he's just 'alright'.
Now, if you are talking about pure vocal talent (NOT popularity, which is what it seems like most posts in this thread are based on so far), take a listen to Joe Nichols, or Marty Robins, or Ray Price. George Strait is also great. Martina McBride, LeeAnn Womack, and Patsy Cline are some great female artists. If you want to go waaaay back, Tommy Duncan of the Texas Playboys.
KA