These beautiful and innocent-looking flowers might be in your mom's window box. They're called Heavenly Blue morning glories, and their seeds can apparently make you trip balls.
This must be a well-kept secret, or more people would be flocking to try such an easily-available high. Technically, the extracted substance (lysergic acid amide, or LSA) isn't legal, but the actual plants are. You can go uproot them from Aunt Myrtle's garden. Go on. I'll wait.
Once you've got your paws on some seeds, you can either eat 100-400 of them straight up, or if you'd like to avoid headaches and heinous gastrointestinal unpleasantness, you can extract from them the LSA using common household ingredients like Everclear. The problem with eating raw seeds are multiple: besides the poison that most shops will douse them in to foil your plans, there is one chemical that will make you nauseous and another that will give you a terrible headache. Either way, the resulting trip is apparently similar to LSD and will last 6 to 10 hours. The flowers can also apparently be made into a tasty wine.
Gee, it sure would be easy to get some and plant them all over town, a la Johnny Appleseed...