The conventional wisdom around winter gardens is centered on the use of structural evergreens. For many, they provide strong verticals and horizontals on which to hang the rest of a design. They can also give you something to look at other than seasonal death and destruction.
For me, they appear as lonely sentinels, guarding the current fashion for leaving perennials with their dead seed heads frozen in the winter landscape. Only a very few plants hold any interest in the dark winter months, and they are worth considering for the city garden.