Saw the Churchfitters at Fougeres this summer. You will probably find lots going on in the little villages - most seem to have a stage and the bigger towns have special days each week when they put on entertainment through the summer. Pick up a free tourist paper when you get there.

Also spent a day at the dance festival at Guincamp (Festival de St Loup) which has dancers from all over Brittany and beyond lots of music as well as dance - they have Soldat Louis every year. Trouble is it's always second week of August. End of July beginning of August is definitely the best time to go - also there is the Blue nets festival at Concarneau and also (although Normandy rather than Brittany) the traverses de Tatihou which is a music festival on Tatihou.

Hope that's helpful

Sarah