I noticed that there are free “guess what” cards at http://www.shop.montessoriprintshop.com/SALE_c69.htm. For example, there’s a close-up picture of a sunflower and one picture from farther away. These cards would probably be appropriate for 2-4 year olds. It’s probably only available for another day or so, but thought I’d mention it here.
Also there are some new free cards at http://www.montessoriforeveryone.com/assets/PDF/From_Plant_to_Food.pdf showing the food and its product (tomato and ketchup, for example).