Black Diamond watermelon (see above) grows well around here, and the melons are nice and sweet. I have the most luck if I thin the herd (no more than two-three melons per vine, the first one gets most of the flavor and size) and just grow more plants. Black Diamond is normally red fleshed, but is also available yellow fleshed, and I'd like to try that this year. I grew some yellow-fleshed variety five or so years ago, and it was fab.
Source for the red (also Moon & Stars, a bunch of others):
http://www.heirloomacres.net/HeirloomAcres/
Source for both:
http://www.rareseeds.com/catlisting.php?cat=32
Christmas lima beans:
http://www.rareseeds.com/catlisting.php?cat=65
Cob Melon (apparently AKA Schweikert's Cob Melon):
http://www.douglasgould.com/amygoldman/New_From_Amy/melons%20book/cobmelon.htm
"Christmas Pole Lima
"The Christmas Pole Lima Bean is a speckled pole lima bean that was first cultivated in the United States around 1840. It is grown for its beautiful seeds which are cream, heavily speckled with deep maroon. The beans have a buttery texture and a rich nutty flavor. They can be used green shelled or dry and they keep their colors even after cooking. The plants are very aggressive growers reaching a height of 10 feet and producing large quantities of 4-6 inch pods each of which contains 4-5 beans. The plants do well in hot and humid conditions."
http://www.landrethseeds.com/catalog/product_info.php?cPath=23_660&products_id=4797