Start out by asking each employee on your team what they would appreciate as a reward. I have discovered some of the best ideas by asking my employees this. It is important that you align the reward with what the employee values - not what you think they would value. I suggest keeping a record of this in their file. Then, whenever you want to reward someone for their efforts check their list.
On a related note, I recommend asking your employees what kind of recognition they prefer - public or private. Taking a moment to recognize someone’s efforts during a team meeting can be the best reward for those that seek public recognition. In the same vein, sending an email that praises the employee to your boss and copying the employee can make someone’s day. For the team member who likes to stay under the radar, a hand written note or card acknowledging a job well done can be the best reward.