The best way to explore the French Riviera ports is on foot. You needn't book a shore excursion unless walking is a problem or you wish to travel to a port other than the one your ship is visiting. If you're looking for something different (say, inland), try one of the following.
St-Paul-de-Vence & Nice (4 hr.; $55): A quick bus tour of Nice precedes a visit to the medieval walled hilltop village of St-Paul-de-Vence, a feudal hamlet that blends into a bastion of rock, its ramparts overlooking a peaceful setting of flowers and olive and orange trees. It offers art galleries and shops, cobblestone streets, cafes, and gorgeous country views.
Medieval Eze (3-4 hr.; $55): Eze, literally clinging to the rocks above the sea, is a medieval village worth exploring. This tour includes a guided walk through the narrow streets, with their lovely restored houses and stunning views. Time is allowed for shopping in the town's boutiques and artists' studios. Visits to both St-Paul-de-Vence and Eze may be combined, for a higher fee, with a tour of Nice.
Nice & Cannes on Your Own (8 hr.; $75): This is basically just an easy way to get from Villefranche to two of the Riviera's major towns. You'll have about 2 hours free in Nice and 3 hours in Cannes. Another version of this tour, at the same price, bundles Nice and Monaco.