Rennes has a large selection of restaurants. The traditional Breton restaurants called 'crêperies' are particularly worth a visit but there are also many traditional French restaurants that you can try.
There is a large concentration of restaurants around Place St. Anne, rue St. Georges, rue St. Melaine, Place Saint Michel and rue St. Malo.
The area behind the métro station 'République' is nice for lunch especially the streets rue Jules Simon ('Le Boudoir' is to be recommended) and rue Vasselot (one of the prettiest streets in Rennes, 'Aux Caprices de Suzette' is on this street and nice for lunch, serving crêpes, galettes, salads and a variety of other dishes).
The following is a link to a useful internet site where restaurants are ranked according to a star system : http://www.linternaute.com/restaurant/home/6/27917/rennes/ or Tripadvisor http://www.tripadvisor.fr/Restaurants-g187103-Rennes_Ille_et_Vilaine_Bri...
Some suggestions for nice 'Crêperies' :
'La Gavotte', 41 rue St. Georges, (02 99 36 29 38)
'La Saint Georges', 11 rue du Chapitre, (02 99 38 87 04)
'La Rozell', 14 rue Penhoët (02 99 78 20 01) (near Place St Anne, nice garden area behind the restaurant to eat outside)
'Ouzh Taol !', 27 rue St. Melaine, (02 99 63 36 33)
Traditional French restaurants :
'Leon le Cochon', 1 rue Vasselot, (02 99 79 37 54)
'La Chope', 3 rue de la Chalotais, (02 99 79 34 54)
'Au bruit qui court', 13 rue St. Malo, (02 99 36 86 86)
'La Taverne de la Marine', 2 place de Bretagne, (02 99 31 53 84)
And if you would like to sample some nice French wine by the glass or bottle, the 'Nabuchodonosor' wine bar is not to be missed (they also serve food) at 12 rue Hoche (02 99 27 07 58).