Any City, Any State, zip
Dear Mr. Smith (can use first name if employee is known well)
Your enthusiasm and your ability to motivate your employees has resulted in a significant increase in productivity and profitability.
ABC, Inc. appreciates your efforts and the assistance you give to your co-workers. If we had an award to give, you would be the key contender.
Please accept my sincerest gratitude for the superior job you are doing in our service department.