Look around for posts about brisket (like at the bottom of this page) from a member named Sawdustguy. He's the competition-brisket-winner-guru around here AFAIK (apologies to any other competition-brisket-winner-gurus around here).
My favorite brisket rub is currently roughly equal parts Bad Byron's Butt Rub, Superfinely ground coffee, and brown sugar. However, if that sounds like too much of a PITA, I'd say go with very simple salt, pepper, garlic powder, and onion powder and really learn the meat/process of a brisket before playing around with "exotic" rubs. If you want to take that 'simple' and bump it up to full rub status, add in some paprika and some sort of sugar