I listen to pretty much anything, so I've seen a variety of different artists perform live. These are the concerts that I have attended that come to mind first. Some of them were at music festivals (such as Farm Aid) and some of them were playing small venues before reaching fame. I saw Taylor Swift for free before she became super famous. I've met Luke Bryan before he was really famous. I'm sure that I am leaving some of the concerts that I have been to out since I can't seem to remember them all so this is not a complete list.
I have seen the following multiple times:
Cher (4 times)
Dave Matthews Band (Over 8 times..I've lost count)
Chely Wright (2 times? I think. I've met her a few times)
Reba McEntire & George Strait (seen both of them twice)
Martina McBride (seen twice)