Thanks for asking me this question. A particular favourite of mine are Epiphllum which are rainforest plants from South America. They have extremely spectacular flowers.
I am also fond of Hoya varieties which come from differing regions of China, Indoniesia and other asian countries.
There are also a lot of rather spectacular bulbs, of course most people know tulips and daffodils, but there are also scadoxis and haemanthus which are very unusual.
Of course what is exotic in one country can be more commonplace in others.
Have just joined HubPages so am really feeling inspired to share my knowledge of plants by writing some hubs soon!