Try the Arbol Sauce at Calexico Taqueria
Calexico (Carroll Gardens, Greenpoint, and a SOHO food truck) started out as food cartists and then opened a brick and mortar in Carroll Gardens after three successful years. This was awesome as the wait at their SOHO cart location often runs into the 30 minute area, while you'll get served right away inside the small restaurant. Inside, you also get access to their salsa bar, which includes several salsas, pickled spicy vegetables and an arbol pumpkin seed sauce. You've still got to order the crack sauce with whichever food you choose though.