The Mexican Tradescantia species are good groundcover plants. They are sophisticated cousins of the weed which plagues most Sydney gardens, Tradescantia fluminensis - better known as wandering Jew - but they are generally not invasive like that horrible one. Tradescantia zebrina (ht 20 cm) is striped in silver and green and has purple undersides, and is more keen than some of the other coloured cultivars to take over your garden than the others, so I confine it to dry shady spots where little else will grow, as it needs minimal water.
Tradescantia zebrina provides an excellent foliage contrast to other plants. It can be effective wandering through clumps of bromeliads to fill in any gaps. I also think it can be useful to cover blank areas where spring-flowering bulbs are dormant over summer. Just remember to pull it back once the bulb foliage starts to reappear in autumn. When it 'wanders' too far, pull up all the bits you don't want, leaving just a small piece: like its scary cousin, it will quickly regrow! It also makes a good subject for a hanging basket if you are too frightened to let it loose in your garden.