Mediterranean Seas (Delphinium tatsienense) from Thompson & Morgan. I started these a bit late, in February or March, but they seem to be going strong in the back of my bed. Not the tallest delphiniums at only 30 inches, but they're an intense blue and they seem to handle the heat with little complaint.
An addendum: This particular Delphinium makes a first-rate cut flower. It looks as good six days after cutting as the first day -- the best vase-life of any cut flower I am currently growing.