Minne-Mama: Color Sorting Toss Activity (with Video!) - Use ball pit balls or bean bags. (I would probably put something around each hole to keep the different colors separate).
Christmas Tree Ball Sort for Toddlers - awesome idea that will keep kids busy, moving and learning colors!
Nuts and Bolts Board: Montessori DIY « mamaguru
Inexpensive way to stimulate the senses. You can even do bubble wrap stomp painting!