Short answer is probably none, as most genuine tropical plants will die in our winter, but......................
There are plenty of tropical 'looking' plants that can grow in the UK.
A few that come to mind are:
Cordyline australis (can get hit in very cold years, but worth a try)
All of the above will give you a very 'tropical looking' garden....without having to protect them in the winter.
A couple of books worth browsing for ideas:
Architectural Plants - Christine Shaw
Exotic Plants - Will Giles
Big Leaves for Exotic Effect - Stephen Griffith
Hope this helps ;-)