I'm going to order a Synsepalum dulcificum, otherwise known as the miracle fruit. The fruit of this tree (bush?) has the distinction of binding to your taste buds after eating it and making sour foods taste sweet. The effect changes lemons into lemonaid without sugar and beer into malt.

It's not well suited to the climate I live in, but I understand if I bring it indoors during the winter it should do just fine. Obviously this isn't the most practical plant to have but the curiosity of it would make it a good addition to my home.