So, what are they?

Ricecakes are a vague relation to the cracker. Ingredients are, typically, rice and salt - the former having been heat-treated so that it expands (in much the same way as with puffed rice cereals) and then pressed into a circular disc.

A ricecake is comparable in diameter to that of a CD, and has about a fingers-worth of thickness to it (though thinner, thicker and amusingly shaped varieties have wormed their way into society now...).

Available from most good supermarkets, and from all health-food shops, 'cakes are a boon for dieters (due to their extremely low calorie content), for those with certain nutritional disorders (most 'cakes are gluten free) and for anyone who wants a break from the traditional cracker or waterbiscuit.

What do I do with them?

Ricecakes will keep pretty much indefinately, within an airtight container. On the downside, however, when left out of an airtight container, they begin to taste like soggy cardboard. 'Cakes can be revived, however, with the strategic usage of an oven on a high-heat to evaporate all moisture back out again (similar results can be obtained with a toaster & microwave combination method, but it's not that advisable - 'cakes burn easily)

Sounds kinda plain...

Some varieties of ricecakes have tried to improve upon their predecessors by including, for example, sesame seeds; so you can have all the fun of dislodging said grains from your teeth. More recently though, attempts have been made to move the ricecake into the general snack & munchies area - by flavouring them, reducing their size, and sticking them in crisp-like packets...   Savoury varieties of 'cakes can be improved considerably by the spreading, or the placing of one of a multitudinous number of toppings. Available to accomodate both the sweet and the savoury, such as fresh fruit, sandwich spreads, or some conserve, with a little work the ricecake can be a marvel of edible delight.