I have just arrived home from Wales and you must take them onto the following:
Machynlleth B4518, follow all the way into the Elan valley and then over the Mountain pass into Devils Bridge, best road I have ever riden, its perfect.
Also just stayed in Brecom and visited a couple of pubs within a village called Talybont-on-Usk, best was the Star Inn, local food and ales. Additionally I stayed at the local Youth Hostel which was perfect just on the edge of the reservoir (YHA Danywenallt).
To be honest I found a great deal of the B roads became single track with lots of blind bends so going wasn't the quickest. Pick the right A roads and you will be fine stay away from main artirray roads and all will be good.
A good sources for places to see is the YHA website and connect to any of the establishments and they generally have local attraction info etc.
Enjoy
Nigel
PS I am going back in May 2013 with a mate it was so good.