This year I heard an ad on the radio about "the hotest pepper in the world" being for sale locally. I picked up 2 plants to try them.
Chinese vegetables can be fun to try. One year I got some Chinese Stringbean seeds. These Stringbeans can get 3 to 4 feet long. While they dont taste exactly like regular Pole or Bush Stringbeans, they are fun to show people when they are hanging on the plants. Other Chinese vegetables are also available in some seed catalogs.
My borther tried growing a White Tomato called the 'Snowball'. They grew and we tried them, but having a acidless tomato is basically tasteless to me.