What dimensions is your garden? Are there areas that get any sun at all? And what soil do you have?
My garden is also north facing and has heavy clay soil. It slopes downwards, away from the house. It's not very big (around 30 m x 6 m) but it's long enough that the area at the end is out of the shadow of the house and gets a bit of sun. So I put all my stuff that needs sun there (the greenhouse, for instance).
I am finding that there are lots and lots of very beautiful plants that love the shade, and that actually, rather than being awful to give up sunny planting, it is a real pleasure to do shade gardening. Try looking at a specialist nursery for ideas - Long Acre Plants is one that I've bought a lot of plants from recently, all of which have been superb. If you can go see some of the famous woodland gardens, that can be very inspiring.
Ideas for wet shade: if it's really soggy, the good news is that you can plant bog plants! Some of my favourites for the wet: ornamental rheum, rodgersia, some gorgeous primulas (lots of varieties, but check out japonica 'Miller's Crossing'), irises (short season, but worth it), adjuga, arums, lamium, brunnera, and ferns, which can be staggeringly beautiful.
In dryer areas, some of my favourites are acers, anemone nemorosa (so lovely), woodruff (a thug in behaviour but dainty to look at), omphalodes, Erythronium (glorious in a month), hellebores (not just the boring white ones, there are lovely doubles now), tiarella, magnolia stellata, foxgloves, box, and shade geraniums (some of which love dry shade).
Oh and lots and lots and lots of spring bulbs - make the most of bluebells and tiny daffs!