Now is a bit late for the best selection, but if you can get hold of pelargoniums (geraniums) they'll do fine, as will begonia (once watered in), marguerites, osteospermums (a favourite of mine as the colours are complemented by the reverse of the petals when they close up out of the sun), gerberas, which are vivid colours, and salvias, for the blue/purple spectrum. I happen to prefer salvias with lavender and they do well together, both the same family and happy in the sun. Some salvias will prefer more moisture at the roots than others, so be aware.

Thanks Worthy1.

I'll see what I can dso for this year and start planing now for next year!

Next year you could try Livingstone Daisies for the front of the border but you don't see them for sale as plants, you'd have to raise your own from seed. Being succulent they withstand drought very well. (But the flowers only open in the sun...)