Thanks - Your Efforts on the Committee
I want to take this opportunity to say how impressed __(I was/we were)__ with the professionalism that you and the entire __(name of committee)__committee demonstrated with the __(type of forum/project/case/etc)__). It was evident that you took the time required to review and understand the objectives, just by the kind of input you offered. Your involvement was both thorough and very well thought out, which gave the other participants in the __(forum/project/case/etc.)__ confidence in any suggestions you made.
Thank you for your valuable contributions on this committee, __(name)__. Your efforts were exceptionally helpful and I want to commend you on a job well done!