Grey plants are usually drought tolerant because they reflect the light and don’t get as hot as other plants so they don’t need as much water.
Grey Leaved Groundcovers:
Tanacetum densum ssp. amani
Artemisia versicolor ‘Sea Foam’
Silene uniflora ‘Druetts Variegated’. Many of the variegated plants like this one have a grey effect in the garden.
Artemisia ‘Powis Castle’
Grey Leaved Shrubs:
Grey Germander (Teucrium fruticans ‘Azureum’)
Eriophyllum lanatum ‘Siskiyou’
Salvia clevelandii ‘Allen Chickering’
Texas Ranger (Leucophyllum frutescens)