The obvious one is Lavender or any of the herbaceous plants with grey leaves as they will cope with the sun and dry conditions. How about trying some of the shrubby Salvias that are available? These come in various shades of blue/red/pink and flower all summer. Try Salvia microphylla varieties for the reds/pinks and Salvia guaranitica for the blue shades. check out Great Comp Gardens website for plants in their nursery. These are all really easy from cuttings, so once you have a variety you can propagate more and more...

This is a great situation for those showy annuals like surfinia, busy lizzie and gazania too. You have lots of choice. I'd mix some of the mixture of water-retaining granules and slow-release fertilzer they sell for hanging baskets as it will be a very dry situation.