Nesting Sort & Stack. I like this beacuse you can sort it based on colors, (dark to lightist) size, (big - small OR tall - short) or you can nest/stack them inside each other or on top of each other. We played with this for a while as it's 'supposed to be used' and then we made a castle.
Shamelessly stolen from a montessori blog we had a plastic spider who was warping things in it's web. So using the ugly green yarn we wrapped several helpless animals practicing some fine motor control skills.
Pouring water! had several different containers we poured back and forth making only a moderately sized mess on the table.