Creeping Speedwell (Veronica) has become one of my favourite ground covers. The bright blue flowers really appeal to me as blue is not a common colour for perennials. It is a low growing ground cover (short can be beautiful!) with attractive foliage, and I REALLY like that while it slowly increases its footprint in the flower bed, it does not invasively try to take over the whole bed by next month.
Everyday Cheer 