One plant that has been quite an unsung favorite in our garden for its fairly unfussy yet interesting ground cover has been the Foetid Hellebore (Helleborus foetidus), we initially planted one on the edge of a gravel pathway in the middle of the garden many years ago, and have been rewarded with a constant supply of young plants growing in the gravel every year.
We have transplanted these with mixed successes, finding it prefers a brighter spot than we often give the young plants. But in the brighter locations it thrives.
One such place is the raised bed by the koi pond filters, where conditions have been a little harsh, a neighbouring conifer in next doors garden provides a rain shelter keeping it much dryer than we had anticipated, most of the woodland plants we had previously tried had failed, however Helleborus foetidus has been a success, filling the edge of the bed and giving the lush feel we were after.
The lime green flowers might not be to everyones taste, and as the name suggests, they are rather pungent when disturbed.
Gaz