Here's a Big Bob Gibson rub I like.
http://www.wchstv.com/gmarecipes/tennesseebarbecue.shtml
For the barbecue rub
1 cup dark brown sugar
1/2 cup garlic salt
1/3 cup onion salt
1/2 cup paprika
2 tablespoons chili powder
1 tablespoon cayenne pepper
1 teaspoon ground cumin
1 teaspoon black pepper
The sauce is great too.