My husband recently added a rail to our cottage deck. It is constructed of eastern cedar, and we applied a generous coat of Thompson's water seal. My husband is concerned about the exposed tops of the upright 6x6 posts. He would like to cap them but does not like the look of most post caps. He is thinking of some sort of was coating. Do you have any good alternatives?

Sounds to me like you have constructed a quality railing. You may want to consider using copper caps and let them naturally oxidize. Alternatively, if you prefer to keep the all-wood look, as long as the tops of the post have not got any major low spots or knots, continue to use a good quality sealant, and they should be fine.