A series of mini-courses on help desk techniques. These would be useful for training new help desk personnel, or helping veterans brush up on their skills.
Various packages vary according to features and functions.
At the very least, the software should be able to prioritize call tickets, sending an alert if a call ticket has been open beyond a pre-determined time length. External support desks share many similarities with internal help desks, which, instead of external customers, support internal employees. Most of the better software packages here let users search the knowledge based using key words. If the problem's solution cannot be found, the call is escalated, perhaps to a more experienced second-level rep. This helps you have valid knowledge on hand even before end users begin calling with problems.