Freida, I would suggest any of the various low-growing sedums, some of which sprawl more than others, and most of which flower in the summer. Other possibilities include ice-plant or portulaca - both flower in many colors, depending on the cultivar, spread, and can be kept as short, or allowed to grow and sprawl as long as you like.

Another possibility, although maybe needing more water and growing wider than wanted, is callibrachoa/million bells - also flowering in many colors. Small-leaved ivies are another possibility.

If you want some height with flowering, try the lower-growing coreopsis - they take dryness well, but do want good drainage. Armeria/Thrift, is another choice, as might be the various thymes or oreganos.