Where do I start? I've got a cabinet full of them.
There are a few local ones that I really like: Hogs 'N Heat, Rustic Rub, Code 3 and Buckhead. And there's a spice shop in Soulard Market at STL that has a few really nice concoctions that they mix up and sell in small containers.
A friend turned me onto a rub from Texas called Rudy's Rub. He buys several at a time and shares them. It's good on just about anything.
Killer Hogs rub is excellent.
I sometimes use Corky's and Rendezvous out of Tennessee, or one of the K.C. rubs, like Arthur Bryant or Gates.