The French Musée des Antiquités nationales (National collection of Antiquities) can be visited in St-Germain-en-Laye, a bit west of Paris. The museum is in an old castle with a nice garden. If you expect the main archaeological finds from France, you will be disappointed: the museum offers a general view of French archaeology, starting in the Stone Age, and continuing to the Franks. (In France, the most splendid finds are usually in local museums.) In the chapel are objects from other cultures, which help you to see the development of Gaul in a global perspective.)
Among the finds are bronze age helmets, iron age cuirasses, several finds from Alesia (this room was closed when we visited the museum), Roman oil lamps, inscriptions, a glass cup with a representation of the Sacrifice of Isaac (this object easily justifies a detour), several statues, and finally brooches and weapons from the Germanic peoples who settled in Gaul after the fall of the Roman empire. It is easy to spend two hours.
Although photography is permitted, do not expect too much of it. The glass displays and the lights are particularly unhelpful. The metro station (RER, line A, Saint Germain) is opposite the museum, where you will also find cheap underground parking places. The museum itself is free.