Answer: "Rock garden" mean different things to different people. To some gardeners it is a label for a special planting of alpine plants or dwarf conifers, for others it is a catchall for low-growing plants interspersed with large rocks.
You might consider junipers, creeping phlox, and sun-loving herbs such as the various creeping thymes. Also wooly yarrow (Achillea tomentosa), pussytoes (Antennaria dioica), Poppy Mallow or Winecups (Callirhoe involucrata), Potentilla, or Veronica spicata. There are hundreds of other possibilities!
As I was searching the Web, I came across this excellent site for the North American Rock Garden Society:
This page has lots of info about rock gardening, and a whole section on good rock garden plants.
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