You can also try roses - Golden Showers, Falstaff, Tess of the Durbevilles will all do well in shade as long as it's got some light and they won't get too big. As with the clematis, you'll need to tie the stems in as horizontally as possible - or diagonally - as this encourages the prodcution of more flowering shoots.
Bothe roses and clems need a lot of food so prepare the planting hole well with plenty of garden compost and/or well rotted manure and water them in well. Roses should be planted with the graft an inch or two below final soil level and clematis should be planted 3 to 6 inches deeper than they were in their pot to encourage extra shoots and to keep them alive should the top die back with clematis wilt.
If that does happen, just cut off all the stems above the ground and give the roots a liquid feed of rose or tomato food and the clem will come back. Clematis wilt is a strange thing which affects the plant from the top down so is easy to recognise and deal with. Clems also need protection from slugs in spring. If you hang a bird feeder on the trellis all year round, you'll find the birds pick off any aphids so you won't need sprays.