I've had a lot of fun crocheting Granny Squares, and made two huge cushions.

Each is 18in (46cm) square, and I've crocheted the backs and the fronts (don't you hate it when the back of a cushion is boring?)

Navy cushion
the front of the navy cushion
the back of the cushion

Rust red cushion

the front

the back, with 'horn' buttons

These were a lot of fun to make! Just google 'Granny Square' for some great free patterns.