canna lilys are good

Acanthus mollis can give a good tropical impression. Perennial Hibiscus (H. moscheutos) is another possibility. Castor Bean (Ricinus communis) is an annual with a tropical kick. Many Magnolia species will look incredibly tropical in the summer, at least, and evergreen Southern Magnolia (M. grandiflora) should work where the winters rarely get below -9º C. Summer bulbs such as Caladiums or Alocasia can also find a use.

Well put Tug - the key word is tropical impression. We don't have the climate sadly.
Musa (banana) could work in a sheltered area. It would have to be wrapped up very well indeed though over the winter.
Gloriosa is a very easy tropical climber. You could start it off in a pot indoors and plant out late May. Lift before the frosts come and store overwinter.

Speaking from experience I hope you have plenty of greenhouse space Anita. I've grown exotics and semi-tropicals for about 7 years and before I learned the beauties of glass protection I lost pounds-worth and still lose about 10% now. All my Cordylines have gone last year and this (see just a couple of questions up) despite fleecing.

This year I have put a couple of Ricinus, which Tug rightly recommends, in pots and am trying them in the cold greenhouse but they look pretty finished to me so I may have to go back to growing it as an annual and new seeds are in the light box now just in case. There is a picture of the 'saved one' on my photo page. If you want to give it a try, I have 3 seeds left. Not many I know but at least one should germinate so PM me your addie and you are welcome to them.

I would try 'tropical looking' plants. For a shady spot try Fatsia japonica. For sun, how about a cream varigated Phormium. Both are very hardy and give the impression of the tropics. Also, try a Trachecarpus palm and how about Eucomis ( Pineapple Lily) in pots. I think a backbone of hardy, large leaved plants would be best with real, tender things mixed in, that way you have it all year round and can try different things each year. Take a look at architecturalplants.com for ideas.