i currently have a boss os-2, and it works well for overdrive and light distortion, but now i want something really heavy to play some nu metal and some other harder stuff. i am looking to spend under or just slightly over 100 us dollars. any suggestions? i currently use an epi les paul standard/jackson dkmg dinky in a peavey heritage vtx.
Get a Metal Zone 2, or the Boss MT-2 (same thing), usually good for heavy metal, but if you are looking for an all dynamic pedal, try the Digitech DF-7, can do everything from heavy to screaming metal! But the thing with digitechs, is they love to drink 9v batteries, so take the time to invest into the power supply. Well worth it.

These are good to find what kind of sound you are looking for and will help you understand what goes into making a good metal sound. Especially the D-7 from Digitech.

Then when you are feeling brave enough, get a Pandora's Box, awesome distortion.
I'd say buy the Electro-Harmonix Metal Muff. I have one of them and they work awesome. I can literally play anything from AC/DC to Pantera on it. Definitely a good investment. Plus its rock solid. Wont break if you ran over it with a F-150. You might wanna get an AC adapter for it though, cause its a royal pain to change batteries out, but thats universal for all pedals. AC adapters are good $5+ investments as well.
Ibanez RGT42DX
-D'Addario .09-.42
Washburn X10
-Ernie Ball Skinny Top Heavy Bottem
Cort 5 String Bass

Kustom Arrow 160FX
Electro-Harmonix-Metal Muff w/ Top Boost

so far iv been doing the sound samples online of them, but i cant test them out till i actually go to a store, but ill be sure to test all of the above. thanks guys, keep the suggestions coming.
If you play with it long enough, and have the right kind of gear, the Boss MD-2 would do a pretty good job of satisfying your needs.. but keep in mind that it wouldn't be able to pull off anything else.