I plan on growing sweet potatoes. Before you point out my truncated growing season, look what I found out:
I became interested in these beauties because they like thin, well drained soil, are drought resistant, and store well at room temperature. They are also highly nutrious and oh so tasty. I found reference to them in an old gardening book (currently on loan so I can't remember the name) about the Ottawa Valley where she says she tries to grow them every year not always successfully but usually has immature tubers to eat which are very tasty. Hunting down the possibilities of season extension, I came across Ken Allan - northern sweet potato guru.
After a year of humming and hawing, I decided that I must try and grow these too. So I have ordered his book and several slips of Georgia Jet.
His article on clear plastic soil warming has me optimistic about melons too.
If this has peaked your interest enough to try it, or if you are succesfully growing sweets in the north, let me know.
Greg Wingate at Mapple Farm supplies short season sweet potatoes and other uncommon veggies, as well as Ken Allan's book:
Ken Allan's page about his short season sweet potato book
Ken Allan also sells sweet potato tubers: