How do I create Credit Memos or Received on Account credits?

How do I save a Credit or Credit Memo to the client so it shows up next time or can be referenced next time they place an order?  A Received on Account payment is a pretty regular occurrence for many businesses and studios for things such as Gift Certificates, Print or Album Credits, etc where the money is received, but the service or product is not yet rendered and tax is not yet collected.  How do I do this?