Can't believe I never typed this. Or did I? No, I don't think so.
Sheldon - INTP or possibly ISTJ, defintely has Aspergers and OCD
Leonard - INTP
Raj - XNXP - Sometimes he seems to have a lot of Fi, doing what he feels like regardless of logic, and sometimes he's more logical. Sometimes he seems more extroverted and Ne dominant, despite being shy. He often thinks of weird ideas.
Wolowitz - EXTP, probably ESTP. Total whore and sensing addict, but also gets excited about the ideas in the group.
Penny - ESFP
Leslie Winkle - INTJ
Leonards mum and Sheldon's girlfriend (aren't they pretty much the same person?) - INTX