If you're in zone 7 or above, and have a lot of room, Gunnera is the plant of choice, with leaves that can easily grow to six feet. It's sort of a tropics all by itself. If you're a bit more pressed for space, try ornamental rhubarb . Petasites also have large, somewhat exotic looking foliage. And don't overlook the accommodating and easy to find hosta as a possibility here.
Most cannas also have the brightly colored flowers so desirable in creating a tropical effect.
Of course those of us in zones colder than 7 will have to dig these up at the end of the season and store them until spring. But canna tubers don't require much care beyond cutting off the foliage and storing in a paper bag in a frost-free space. For a hardy alternative, try variegated horseradish . Next you need spiky plants. Yucca filamentosa fills the bill quite nicely for gardeners in zones 5-9.