MCR, PAN, MRE, MBN, WSA, are the main producing ones, throw in IGO & KZL for Nickel as other producers with Nickel projects
I like CZN in the advanced explorer ranks (JORC resource), others to watch for include MLM (Nornico project), PRW/MFC, & RXL
I like MRE as a pure Nickel/Cobalt play, plus MCR for its move to other metals as well as Nickel