A plastic bowl
Your baby will love when you... Hide a favorite toy underneath, making it appear and disappear.
She'll learn... Object permanence -- the idea that objects still exist even when she can't see them. Fair warning: Your baby can play this game for hours; you may feel ready to go insane but she'll roar with each big reveal.
A sponge and wide-mouthed plastic jar
Your baby will love when you... Tear a new sponge into large pieces and show her how to put them in the jar and dump them out.
She'll learn... Fine motor skills, sensory awareness ("Oooh, sponges are squishy!") and the concept of in and out.
Empty tissue boxes
Your baby will love when you... Stack the boxes and knock them down. (Don't worry if you're still doing all the knocking over!)
She'll learn... The concept of up and down.
Your baby will love when you... Turn off the lights, and shine a flashlight on a wall (not directly in your baby's eyes, of course).
She'll learn... Eye strength. Following the light will strengthen her eye tracking skills and muscle coordination.