Don't much like the texture of rice cakes, but a great alternative are corn thins, by Real Foods. Same size, slightly thinner, lovely and crunchy.
They come in various varieties - my favourite is sesame. (The lemon and pepper one is pretty awful, in my opinion.)
You can have five for a HEXB, or syn them at 1 syn each.
Waitrose and Tesco sell them, probably other supermarkets as well. Usually to be found next to the rice cakes.