Sometime the plants you don't think of as flowers are very valuable to bees. Ivy is particularly important for honey bees, as it flowers in the late autumn when there are few others sources of nectar for them to build up stores for the winter. So if you have any wild corner where you can let ivy romp away, that will help the bees.
Honey bees are also fond of some of the small-leaved evergreens such as cotoneaster and lonicera hedges, where the flowers are almost invisibly small to our eyes. I'm not sure if these are native, but they are good for bees.
Oh, and they simply love oil-seed rape, and get masses of nectar from it. Is there a competition for the least popular wildlife-friendly plant? 