I like your idea of combining drought tolerant species, I have toying with this idea myself for awhile as I have several possible candidates. Before I list them let me say that I think you should research using cacti with Aloe vera. Although Aloe is drought tolerant it may not be as much so as true Cacti. Just a thought as I have only a little experience with Cacti.
Some plants that I have been considering for such a dish garden are, clockwise from center:
Haworthia fasciata or 'Little Zebra Plant'
Crassuala sp any of the 'Jades' or even Portulacaria 'Baby Jade'
Scilla violicea I know of no common name for this plant.
All of these require little water but need more than cacti. The first and third are not terribly tall so consider what such a composition might look like.