Don't know how long or high the slope is but try Daffodils, primroses, foxgloves, euonymus fortunii. Vinca both Major and Minor, camelia at the bottom of the slope, azalea ditto if the soil is acid, most hardy herbaceous geraniums, pulmonarias as long as it isn't too dry, ferns (some will stand dry conditions) euphorbia robbiae (a red leaved one whose name I forget but isn't invasive though it seeds itself nicely). Other people will have more suggestions.

You could add a splash of foliage colour with some heacheras these will give you colour all year round and flowers in the summer, a mix of these with all those different leaf colours of burgundy, yellow ,peach, green etc will give you the wow factor.

It might be nice to have some scented plants such as jasmine, lavender or honeysuckle under the windows.