Cloud Computing is a new paradigm which allows individuals and organizations to purchase resources like compute, storage, networking etc as a utility with minimum human intervention. According to recent surveys more than half of the large to medium size organizations have already migrated to the cloud. Despite of providing resources as a utility and its wide spread acceptance in the IT community, cloud computing is still at its prime and poses many challenges like automated service provisioning, virtual machine migration, server consolidation, energy management, traffic analysis, data security, software frameworks which needs considerable amount of research to stabilize. Conducting research on live cloud environments for individuals or small institutions is very difficult due to the costs involved in setting up a cloud. This paper presents various cloud simulators which were developed over the years that are a cost effective way of conducting cloud research tasks. This paper compares almost 17 cloud simulators based on diverse criteria and the result and explanations are presented which enables new researchers to choose a suitable cloud simulator.