Dear …
RE: __(Reference Name/Number)__
I want to take this opportunity to say how impressed I was the professionalism __(name)__ demonstrated with __(his/her)__ contributions to the __(project name)__ project. I found that__(he/she)__ was exceptionally helpful on this __(case/project/etc)__, willing to help in anyway __(he/she)__could. __(He/She)__ made my job a lot easier and was a pleasure to work with.
__(Name)__ displayed willingness to take the time to review and understand this __(case/project/situation/the customer’s needs/etc.)__ in detail. __(His/Her)__ involvement was both thorough and very efficient, which gave me confidence in __(him/her)__ with any of the suggestions __(he/she)__ made. In addition to that, __(he/she)__ proved to be an excellent liaison between __(name the parties involved)__ and did whatever __(he/she)__ could to expedite the process.
I must commend __(name)__ on __(his/her)__ outstanding job. __(He/She)__ is an excellent representative of __(name of organization)__.
Sincerely,