Funnily I thought i had already posted on this topic...
This is on my patch, I would recommend in no order:
Mont St Michel (get there very early as it gets swamped by tourists), Dol De Bretagne, Cancale (yummy oysters), St Malo, The rance river including all the small villages - unless you are interested in the engineering aspect don't use the tidal powerplant to cross the river but use the old bridge in St Hubert - Dinan, Dinard, Cap Frehel, Fort La latte, Dahouet. If you want easy miles there is a canal with a towpath from Dinard to Rennes.
I will be around some of this week, but don't know yet which days I will be free...