Something trailing over the edges would look nice, various alpine type plants trail, so do phlox, erigeron glauca would be 'my' choice i think - google it and see what 'you' think.
I suppose you could choose annuals too if that's your thing.

I've got two old chimney pots, either side of the front door. Instead of just planting up the chimney pots, I put plant pots inside them. At the moment, one's got flowering pansies in it and the other has a hosta. As they're in pots inside the chimneys I can change them with the seasons, i.e. replace the pot with something else when the current ones start dying off. That way you permantly have something attractive at the front door!

I do the same as Sheilar with 2 pots either side of steps in the back garden steps. I have heucheras caramel and creme brulee doing very well in more or less full sun. Those woven hanging baskets balance well on them too and shallow rounded pans of sempervivum as well. The pots will last much longer if there is no soil in them. Some of mine I have had for about 40 years.

thanks for the ideas for my chimney pots, im looking into all of the plants. thanks again.

hi i have 2 chimney pots in the front with pots inside at with trailing petunias in ideal as the slugs cant munch away on them and petunias just flower amazingly well .... bet your chimney pots will look brill . alison