The Center for Disease Control (CDC) lists three categories of biological agents which may be used as bioweapons: Category A, Category B, and Category C.

Category C includes “emerging infectious disease threats that might at some point be engineered to produce biological weapons.”

Category B includes potential biological weapons listed by the CDC as being moderately easy to disseminate. Each of these includes possible threats that are not of extreme concern to the United States, so we will therefore only be concerned with Class A bioweapons; these pose the greatest threat to the United States

Category A includes “anthrax, smallpox, plague, tularemia, botulinum, and viral hemorrhagic fevers.” (Source)

More information on Category A biological agents