I recommend the DiMarzio Super Distortion. Its a 4-wire humbucker that can be wired to a switch for series or parallel connection of the coils without losing the humbucking effect.

In series, you get a classic, heavy, 'bucker sound suitable for Sabbath and Aerosmith. In parallel, you get a really good blues tone that sounds like a hum-free Strat with a little more upper midrange.