Play ball Attach a soft ball or small stuffed animal to a bright ribbon and dangle it above his head, letting him swat and kick at it. (Just be sure to never leave him alone with the ribbon.)
Music makers Join him on the floor with several bowls and spoons for an impromptu drum lesson.
Simon says Place him on the bed. Touch his nose and say "nose." Put his hands on your nose and say "nose" again. Repeat with other body parts.
Dump truck Give him a shoe box filled with blocks, rattles, plastic rings, and other small baby-safe objects. Sit next to him on the floor and help him empty and fill the box over and over.
Bubblicious Blow a cascade of soapy bubbles so he can reach up, try to touch them, and giggle.
Mirror, mirror Sit in front of a mirror. Sing songs, talk, and make funny faces together.