Same as those above, I wing it, the goal always is to have a "bite", some real discernible spicyhot to the mix.
Dried habanero accomplishes this, found it in a granular type "powder" form one time....I believe that this was at the Mexican Swapmeet, 35th ave + Buckeye.
That was a beautiful thing, re: rubs and just spicing up foods in general I should have bought more, much more.
With where you live Dan, theres a BBQ Store a couple miles North of you that has recently added an amazing rub....I forget what its called ("Naked" something, I thought) and understand people wanna make their own rubs but were one of a mind to get a premade, that stuff rocks. Spicy.