Herb garden
Seeds, pots, gardening tools
Easy board game
Books
Sit and Spin
Craft things
"Coupons" for doing cool things with mom/dad, like making homemade butter, making cookies, making new playdough, coloring eggs, playing chase outside, etc.
A globe or map
I suppose it depends on what the child is into, really. Big hits for my 3 yo:
Play fabrics to be used as tents, dress-up, blankets, etc.
Schleich animals
Farm set with homemade playmat
Spices to make "soup" with in water
Stuffed animals
Wooden beads (she uses these as play food for her stuffed cat)
Play kitchen supplies: The biggest hit at our house is the spice rack that I filled with containers of dry pasta and beans to use as her "ingredients"
Chin-up bar for doorway (dd is a natural climber!)
I try to buy things that aren't "age specific" because I have no desire to buy lots of new things each year.