To me OpenStudio, the free E+ GUI from NREL, is really the tool that has drawn my attention on cloud computing. Within their Parametric Anaysis Tool (PAT) they offer a simple "plug and play", GUI-based way of using Amazon EC2 to compute multiple simulations.
But this is definitely not the only way of using cloud computing. You can do it with the bare version of EnergyPlus coupled with JEPlus, and that has been true for a long time (see this video from March 2012).
Also please note that Amazon EC2 isn't the only solution to cloud computing. DesignBuilder (DB) apparently has, I believe only since their recent v4, a Simulation Manager that allow you to use another cloud computing solution called JESS (I cannot comment on it as I have never used DB). JEPlus lets you do that too, but DB being a GUI, I figure this would be the closest alternative there is to the OpenStudio PAT.
And if you only want to run multiple simulations, you could also simply run them on different cores of your computer, or on a local network server.
Is this question about EC2 specifically--and in particular about running simulations on your private EC2 account--or is it about simulation on the cloud in general?
@Amir Roth, my question is about running simulations on cloud in general.
@Monika Sharma. Sorry, one more question. Are you looking to use the cloud to offload individual hand-crafted runs or to perform larger parametric studies like sensitivity analysis, design, optimization, calibration, etc.?
@Amir Roth, I am interested in using the cloud to perform parallelized simulations or to run hundreds of instances at one time.
@Monika Sharma - can you choose an answer to the question based on the choices so far?