Wild Geranium (Geranium maculatum) retains its attractive foliage all season long. Long-lived, it expands slowly to form a nice clump. Prefers shade, but will grow in full sun in a rich, slightly damp soil.
Geranium sylvaticum 'Mayflower', another for full shade. A very lovely form, late May flowering and intermittently later. Native to the UK and most of temperate Europe. This is a large flowered form with blue/purple flowers with a white centre.