Adapted from Alton Brown’s “formula.”

1c brown sugar
6Tbsp kosher salt
2Tbsp chili powder (get the good stuff or make your own)
1tsp onion powder
1tsp garlic powder
1tsp ground black pepper
1tsp cayenne pepper
1tsp ground mustard
1tsp thyme

Mix thoroughly, rub into a rack of ribs, let sit for several hours before smoking.

//edit: whoops, that should be 2Tbsp chili powder, not 1Tbsp.