I'm currently designing a front garden in North London for a client who loves exotic, tropical foliage. Its really exciting to be able to use some unusual and beautiful plants. One plant I've been wanting to use, ever since I saw it in the tropical garden at Great Dixter, is Amicia zygomeris. It is a woody, deciduous perennial which has interesting, heart shaped leaves and unusual purple pea-like flowers in early Autumn. Although it is cut down by a hard frost it can grow up to 2m in a season in good fertile soil. it has an upright habit so can give height to a scheme without taking up too much space.
Another plant that I'm always excited about using is Euphorbia mellifera. Although slightly tender, it can grow into a 2m x 2m shrub in a sheltered well drained spot. I love the fresh green, lance-like leaves that look good all year round and the honey scented, reddish -brown flowers that appear in spring. If you don't have space for such a large shrub, you can try Euphorbia stygiana which has a similar habit and foliage but only grows to 1m in height.
Have a look at my Tropical Gardens Ideasbook on Houzz.com to see more planting suggestions for a tropical border