I just googled this plant...isnt it lovely?...one called 'black magic' is a super plant...Can grow up to 5ft tall with equal spread..heart shaped black to dusky purple foliage ..nice with silver, or red plants...' .Elephant ear' can also be grown near water as it likes high moisture....Perennial... and can be grown in sun or part shade...Rich, well drained soil and lots of water....Starting tubers off in a green-house, plant tubers 3-5" deep (7-13cm)...Fertilise weekly, re-pot each year if grown in containers, lift the tubers and store over winter...propagate by division....Beautiful...:>)

Another very tropical looking plant is Ricinus Communis, Zanzi Palm (obtainable from Chilterns) which will grow to 12 feet or more in good conditions (as an annual of course). Very imposing plant which creates very tropical look.

Also check out Cannas and Gingers - both rhizome/corms, treat similarly to Colocasia (and have a look at Alocasia as well)

If your local library can get hold of a copy of 'Encyclopaedia of Exotic Plants for Temperate Climates' by Will Giles, you will find this very useful. It was published in 2007 so should be readily available