You know, I have to admit I'd be cringing every time I stepped on my plants!
(A few stepping stones, log slices, bark paths, etc. would make me feel better.
It would allow using taller plants, that might otherwise get damaged quite a bit, too.)
Assuming you are looking for shorter plants...
Lysimachia nummularia (excuse the meter on the side of the house; I've never figured out how to hide the darn thing!):
No doubt you've already considered Ajuga reptans? It's another that can get to be a pest in warmer zones but is a very useful and reasonably slow-spreading groundcover here.
There are a zillion cultivars but here is Ajuga reptans 'Valfredda', one that I like a lot:
The lower-growing Antennaria species (pussy-toes) can be very nice, and even the flowering stalks are only a few inches tall.
Antennaria umbrinella:
Another Antennaria whose name I've lost, unfortunately:
Groundcover Veronica species would probably work well.
Veronica saturejoides; this is not a great example of Veronica whitleyi but it does nicely around here; a variety of V. repens(?) or similar whose cultivar name I've misplaced:
Many thymes do well here, not just wooly thyme... and it does smell nice when the foliage is bruised!
Thymus neiceffii, in bud and in bloom; Thymus doerfleri; Thymus 'Pink Chintz:
Thymus minus - excellent for between stepping stones; Thymus serpyllum (x2) - a good late summer bloomer, love watching the bees enjoy this!
How about Phlox subulata, of which there are many cultivars; also, Phlox stolonifera is low-growing with flower stems to about 8"... ?
