Hugo Peeters has a nice script that can help you identify configuration problems with a VI cluster. To give a common configuration problem, if you put a bunch of ESX servers in a cluster and one of them does not have access to the same shared storage as the others, it will cause problems for DRS. Hugo’s script helps you identify these problems before they bite you in production.
Also, Cody Bunch has a script to query and answer VM questions. VM questions are those seldom-seen dialogs in VI Client that pop up when ESX decides it cannot safely continue executing a VM. This can include changes that prevent startup, like in Cody’s blog, but VM questions can also happen at runtime, for instance if a VM with a snapshot attempts to write to a full datastore.