Shrubs - Mahonia, Viburnum bodnantense, V. tinus, Prunus subhirtella (though that makes a tree, if you've got enough time)
Perennials ? mind's a blank at the mo
Others - ornamental cabbages, winter flowering pansies, cyclamen (my faves) especially C.coum, polyanthus flowers very early in the spring.

Early flowering Crocus, Narcissus, Snowflake, etc.
Winter Jasmine, Flowering Witch Hazel, Kerria (bright green twigs), Coral Dogwood (bright red or yellow twigs), Dwarf Blue Arborvitae (Platycladus orientalis 'Minima Glauca', turns a soft lavender in winter).

mahonia pyracanthas