The Indopedia has this handy list of famous fictional chemical substances, broken down by entirely fictional elements, fictional isotopes of real elements, fictional properties of real elements, fictional compounds and alloys, and fictional medicines or drugs. Required reading for any supervillain in training.
Besides classics like Adamantium, Dilithium, Kryptonite, and Mithril, you've got such lesser-known precious materials as Ununpentium (supposedly powers UFOs), Agatean (magic-proof explosive from Discworld), Naquadah (with which one builds and powers Stargates), Scrith (from which one builds Ringworlds) and Thiotimoline (a drug which Isaac Asimov used to mock self-serious scientists).
Wonder how many of these I can cram into the list of words every science fiction fan should know?
Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can also follow him on his personal blog.