One of my most favourite plants in the garden is Gaura lindheimeri, Whirling Butterflies.
Gaura means superb, and this plant truly is. Flowers appearing along delicate stems in succession throughout the summer. In fact it goes on for months and needs no deadheading!
This plant is great for filling gaps in preferably well-drained soil, although mine seems to like a little mulch around the roots. It is a native plant of Texas and Mexico, where it is plentiful. It needs a good space and in my garden I have allowed for a two foot spread and height, although this is only approximate.