We dropped into the Breconshire Brewery the other day after a walk up Fan Y Big. Couple of v friendly chaps sold us some lovely beer at a very good price. Well worth a visit.
Our local CAMRA lot are doing an all day coach trip from Swamsea to Brecon for that very purpose, on November 20th. Can't wait!
Believe the plan is to visit the Red Lion Penderyn -- mentioned by dynamicbaddog earlier -- on the way back. It's truly a grand place, we've been several times and it's excellent, lovely atmosphere. Fires on a cold winter night too!
Another remote/hard to get to but highly recomemnded alehouse is the Ancient Briton, Penycae (upper Swansea Valley)