Groundcover. Gardeners, this is the year I finally put in proper ground cover. I have ajuga in one contained area, and I love it, but boy, is it a bully -- it is beating out all the other plants there. Don't think I want it anywhere else. I have some sweet woodruff -- a bit slow spreading, but so far, well-behaved, and the white flowers are pretty. Not sure I want it everywhere, though. I have a very dry bed near the street, and some more normal beds that are quite large.
What are your favorite ground covers to mix with perennials (such as hostas, ferns, etc.) in a shady bed? How about a sunny one?