DS-1 by Boss would be my choice. The guy from U.K. Subs uses Metal Zone combined with other Boss effects, but if you're into real punk, you need something much crappier. Try some cheap distortion pedals, or have an electronically literate friend make one for you ( or DIY, for the maximum crappiness factor).
Impendance is fruitfull
while the buttons are circled.:eek: