Some simple gestures of encouragement would definitely do, like a simple pat at the back or a good uplifting conversation over a cup of coffee. Applause them at an instant for a job well done while the achievement is still fresh in everyone's head. Do not wait for the annual gathering to recognize your employees. It's always effective to be prompt.
Stepping up a bit, I think to give employees a good working environment is a great motivation for them to work hard and not to stress themselves working. I used to work in an office that is lacking a conducive atmosphere to work and it stressed me out a big deal. It could be degrading morals. A good working environment encourages a positive attitude for employees. It's their workplace, they spend a huge amount of time in there. So, it's only fair to have it comfortable for employees to stay.
Social gathering is good too like a staff Christmas party or Halloween Costume Day at work. It promotes camaraderie at the work place and the costume day at work is really cool.
To promote and support some charitable works is also a good way to motivate employees. Sometimes, its the employee themselves who initiate this and its always best for the company to give their support for the cause.
Deeds not words --they say is the best motivational approach.