Perhaps the most exotic-looking plant I know of is the Banana tree, and you can be sure I will be growing a couple if I ever truly believe that our greenhouse will be finished. And of course there are all manner of palms that do nicely in the house but will not object to a summer outdoors.
Caladium come in wonderfully tropical colors, from a cool green and white to a shocking pink, red, green and white combination, and can be inexpensive enough to plant as annuals, or to try to overwinter as pot plants.
And finally, try a Brugmansia. You can buy one relatively inexpensively in spring - a tiny plant of about eight inches in a quart pot which will, by summer's end, reach five feet, if happy. I have been planting mine out and digging it up every fall to spend the winter in my sunroom, but recently discovered that I would get more luxuriant bloom if I left it in the pot and let it get potbound. It already is pretty impressive with its long, droopingly dramatic fragrant trumpets - but a brug in full bloom is an astonishing sight - so mine stays potted from now on.
So unless you live in a really cold zone, there really isn't too much digging and hauling to be done to achieve the effect of a true tropics in a temperate zone. It just takes an eye for shape and color. The main thing to remember is if it looks tropical to you, use it. This is your getaway, and whatever helps you feel exotic is a good plant for your personal paradise.
Read about The Plantfinder's Guide to Tender Perennials, a book that will make creating a subtropical paradise a cinch!
For another take on tropical gardens for temperate zones, try Giverney Gardens
Exotic Plants in a Cool Climate is another great source for ideas.
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