I am currently attending most markets ad hoc so not much point putting them here just now.
My one regular spot is Llanyravon Manor Rural market in Cwmbran on the last Sunday of every month. The manor itself is worth a visit with a nice tea room and there are outdoor events throughout the year some of which the market coincides with.
There are between 10 and 30 stalls attending this market at various times with the most stalls being from September to December.
Well worth a visit if you have a free Sunday afternoon and fancy a little fresh air.