I've got some nice blooms on my Aconitum napellus (monkshood) this year. I dug this plant out of my sister-in-law's yard, so that I could admire it and keep it away from children that might try eating it. This is a nice plant for late-summer blooms, though the dark blue doesn't stand out from a distance like bright whites and yellows do.
Aconitum contains toxic alkaloids that are cardiotoxins and neurotoxins. These are found in all parts of the plant. It is interesting that it is used in homeopathy and traditional Chinese medicine. Canadian actor Andre Noble apparently died in 2004 after accidentally ingesting the plant while camping in Newfoundland. Plant toxins will cause symptoms in the cardiovascular, neuromuscular, and gastrointestinal systems, though death is almost always because of cardiac ventricular arrythmias or asystole ("flatline", a ceasing of electrical activity in the heart).