The new Raspberry Pi Zero W has been announced just in time for the fifth birthday of the Raspberry Pi. The Pi Zero adds on-board connectivity (Wireless LAN and Bluetooth) which really extends the scope of what you can do with this board. All for $10.
There's also an official case with 3 different lids: a plain one, one with a window for GPIO access and one with a camera hole.
Check the Raspberry Pi Zero W announcement post for stockists.
Pimoroni have some great Pi Zero W project kits. (We've been enjoying programming their Flotilla Dock and Modules with Scratch recently.)