Just saw this thread, it's hard to narrow it down! I do have some upbeat favorites that I listen to while I walk...
Natalie Grant (I will not be moved)
Nichole Nordemon (Brave...and just about everything else she does!)
Steve Curtis Chapman (I do believe)
Addison Road (Sticking with you)
Barlow Girl (No one like you)
Particularly love the female artists above b/c they're in my range and I can sing along...hard to do when you're trying to run, but helps pass the time!

Blessings!