It looks like BLR has a number of sample performance appraisal forms under the Performance Appraisal topic (http://hr.blr.com/topics.aspx?topic=126), but you have to be a subscriber. I don't know where else to get actual forms.
I agree with SFbay that managers and supervisors should be trained to have enough "day-to-day" contact with direct reports and give them enough feedback and constructive criticism that come time for the actual performance evaluation/appraisal, not much of what the manager says should come as a big surprise to the employee. If the employee is genuinely surprised or blindsided by a negative evaluation, the manager is not doing enough in terms of communication.
I'd like to add that when you conduct training, you should also make sure all managers understand whatever rating system you are using (assuming you use one). If you have a manager giving scores that are way out of sync with the rest of the company (this usually, but not always, comes in the way of a manager that gives everyone scores that are too high) it is harder to reign that person in after they are in the habit of doing so. It's better to make sure you train everyone up front when you implement a new system (OR train each individual manager you hire for a system that's already in place.)
We just modified our rating system, and it resulted in some rather significant changes in the numerical ratings employees received, and the meanings behind those numbers. We learned that it's very tricky to roll out a new system and you really need to make sure that it's being communicated not only to managers but to employees what your ratings signify, or else confusion can result. For example, we had a 5-point system where many employees were used to receiving "4"s to show they were doing what equates to a "commendable" job, while "2" meant you were doing a "marginal" job. Now, we have a 4-point system where a "2" means you're doing a commendable job. But after years of associating "2" with something negative, trying to sell that concept to our employees was understandably difficult.