The Little Man Computer (LMC) paradigm was developed at MIT during the 1960s where it was taught to all undergraduate computer science students. LMC consists of a cartoon character inside of a walled room containing mailboxes, a calculator, a counter with an external reset switch, and input/output baskets. Although this analogy between the internal operations of a hypothetical computer and a real computer is not perfect, LMC has proved itself enduring, intuitive, powerful, and an extensible teaching paradigm. In this paper we present a range of visual LMC simulators from K-12 to post-graduate educational levels. In particular we highlight four simulators in detail: (1) a K-12 interactive CD-ROM LMC tutorial; (2) an undergraduate web-based LMC Shock-Wave animated simulator; (3) an undergraduate web-based LMC Java simulator; and (4) an extensible undergraduate/graduate LMC/Postroom computer. Together these simulators provide a powerful selection of tools for illustrating the concepts of computer systems architecture