It's all about your price range. Maybe look into some overdrive pedals, along with MAYBE a distortion pedal. I don't play heavy metal, I play classic rock and Christian worship music, but I can tell you my dirt pedals. I have a TC Electronic Dark Matter distortion pedal, a JHS Morning Glory overdrive pedal, a Mad Professor Golden Cello overdrive pedal, and a T-Rex Crunchy Frog. The Crunchy Frog is great because it is so cheap, yet so good. It's only like $85, while most of my other pedals are $150-$200+. You may also want a boost pedal, to boost your overdrive. The Crunchy Frog has one built in, but I also have a second one that I use to boost volume instead of overdrive (it depends on where you have it in the chain). I have the Mad Professor Ruby Red Booster.