Jimmy,
If you are staying at one of the Disney Hotels, they should have a luggage store. Most of them (well the 3 that we have used so far certainly do) have a facility where you either collect later in the day, or if travelling by Eurostar, you collect them from the luggage drop at the train station.
Other than that, as previously mentioned, the Guest Relation window on the right-hand side of the park entrances is an option, though I suspect this may really only be practical for hand luggage sized items.....and as rightly stated a small fee applies.