Dear …
__(Date)__ will mark your __(#)__ anniversary as an employee with __(Name of Organization)__. In recognition of your dedication and __(loyalty/commitment/etc.)__ to our __(firm/organization/company/etc)__, please allow us to offer to you, a small token of our appreciation. This __(type of gift)__ is our way of thanking you for all your valuable contributions over the past __(#)__ years.
We know that the growth and success of our organization depends largely on the capable staff we having working for us. It is a pleasure to have you as part of our team. __(Name)__, and we thank you for your part in helping us maintain the success we currently enjoy. And in looking to the future, we hope that you will remain with us for many years yet to come.
Congratulations on your __(#)__ anniversary with __(Name of Organization)__. We are proud to have you on board with us.
Sincerely,