Everything! Singing, dancing (with and for her), exersaucers, rolling around on the floor, explaining everything you are doing, and also playtime in crib away from mommy and with mommy. Mobiles, tupperware and other stuff she can practice manipulating with her hands, peek-a-boo, this little piggy, ride a little pony, or even just spin around with her in your arms. Grab her by her hips and hang her upside down for few seconds - it always terrified me when DH did that, but it's actually good for brain development; it's called vestibular stimulation. HTH
Crystal