Preschoolers learn best by doing, hands on learning: puzzles, blocks, lacing cards, Play-dough, etc. the list is endless. Toys and activities that stimulate, also educate. Nearly any daily activity can be used for learning. When I am cooking I let my daughter help measure, when I am doing laundry I let her help identify colors as I sort clothes, and when I place my throw pillows on the couch ask my daughter which color pillow goes next in the pattern. She benefits from me taking a little extra time in what I do.
My preschooler loves anything she can eat. We make organic cereal necklaces, edible play-dough with peanut butter and grow plants she can derive veggies from to name a few. She loves painting anything especially finger painting. I tie painting into some other subjects to make it more beneficial. We paint a penguin, talk about God creating the birds and then talk about where penguins live. The library is a good aid in finding books to help keep kids interested. I use a fun fictional penguin story as an added bonus. The book Montessori on a Shoe String has a lot of really good ideas; it is available from Catholic Heritage Curricula.