They are different.
我看 = I think but sometimes "我看" has a simplified usage like "我看行!" which means I think it's ok! And we don't say 我想行
我说 = I say and sometimes it means "what I want to say is" ... like "我说,能不能借点儿钱给我。"
我想 = I think that. It is often followed by a complete sentence not a phrase.