Re: "prime" monads?

Has someone already mentioned that Eilenberg-Moore algebra categories and Kleisli categories "coincide" for all idempotent monads? The forgetful is full. Ross

There ARE a few monads for which the Kleisli and E-M categories "coincide," however, beyond the identity monads. First example coming to mind is the FreeVectorSpace monad on SETS. I'm sure other Categories-readers will point out more.