We use CoverMyMeds.com to complete prior authorizations. Staff can start the authorization, filling out as much information as possible, then notify the provider a request is waiting. She logs in, answers whatever questions staff couldn't, and clicks a button to automatically fax it to the insurance plan. It's easy to use, and we can archive requests once they've been approved/denied so they're available to reference next year when we're asked to complete another PA for the same med.
Of course our preference would be for insurance companies to stop playing games with our patient's medications, but if we have to do them we've found this is the easiest and least time-consuming.