The washing machine. When tiny, he used to watch it. Now, I give him a pile of socks and (clean) washable wipes, and he stands and puts them all in, shuts the door, presses some buttons, claps, opens the door, takes them all out, puts them all in again... He is 15 months.
Another one that loves the balloon whisk here, too. And the tea-strainer.
Keys on a keyring with a very chewable leather key fob.
Pieces of white card with faces drawn on in thick black pen.
A wind-chime.
His older sister's toys, particularly her cooking things. Those plastic fruits with the velcro in so they come apart. Plastic plates and spoons and cups and saucepans. I wish I'd bought them for dd when she was 4 months rather than 2 years!
Ds had a happy 10 minutes with a pile of cd-roms yesterday, until dh caught him (they were the latest computer backup). Might have to put some blank ones in a box for him!