The RP's (from Digitech) do metal well on the HAIRDY effect. My other guitarist and I both own an RP250, which have the HAIRDY effect on it. Either that or the FUZKNG effect work well for metal over ska. That's just what I like to use.

Boss makes some good distortion effects, but you could get a distortion pedal from pretty much and effects company.

Good luck on getting the sound right.