I like Maitre Kanter in the Jacobin square, plus l'Auberge des 7 plats and Patagruel, both the latter in the old town. The Corail by the station is also good, frequented by one Huge Chamberpot, so can't be bad!
North of Le Mans, try Fresnais sur Sarthe, lovely little chateau and a good place to wander about, plus the little manor house mentioned in my first response.
Le Lude is good, plus, if you have never been although a little further afield, Chateaudun - a good taxing walk around the (very) steep old town. We often take visitors there and the response is always good. There is a good circular walk of about 10 ks round my own village. If this is your bag, pm me and I'll try to find a map for you.