Have you tried any of the Japanese Morning Glories? There are some real beauties, but they take a bit more care. I really like this one, the variegated foliage is pretty in and of itself:
Japanese Morning Glory (Ipomoea nil 'Yoi no Tsuki')
Another that is really striking is the Blue Shibori. (Swallowtail Seeds sells them as Venice Blue ). They're one of my favorites.
