I used 10 eggs for the Honey and Treacle tart on Saturday. While I was cooking the tarts I dried the egg shells too. That way you can store them and deal with them later without them smelling. I learnt that the hard way one summer.
After that all you need to do is crush them with a rolling pin and you can throw them in the compost, use them as a barrier to stop slugs or put them in the wormery.