Rice milk can be made with beta amalyze an enzyme derived from barley which is chametz.
The following brands of OU Kosher pareve original or plain rice milk do not contain any chametz, but are kitniyot:
Clearly Organic
Full Circle
Harris Teeter
Hy-Vee
Market Basket
Meijer
Nature’s Place
Nature’s Promise
Price Chopper
RicePure
RiceSense
Shop Rite
Wild Harvest
Wild Oats