Anthrax 
Anthrax is a bacterium with a highly resistant spore form. It is highly infectious and lethal when inhaled. It is a non-contagious disease which does not spread from one person to another. An anthrax vaccine does exist but requires many injections and has enough side effects that it is considered unsuitable for general use.
Smallpox 
Smallpox is a highly contagious virus. It transmits easily through the atmosphere and has a high mortality rate (up to 30%). Smallpox was eliminated in the world in the 1970s, thanks to a worldwide vaccination program. However, some virus samples are still available in Russian and American laboratories. It is also believed it could be available in other labs. Although people born pre-1970 will have been vaccinated for smallpox under the WHO program, the effectiveness of vaccination is limited since the vaccine provides high level of immunity for only 3 to 5 years. As a biological weapon smallpox is only transmitted to people that are in close proximity with someone who has been infected with smallpox. Smallpox only occurs in humans and transmitted between humans, there are not vectors or reservoir hosts.
Botulin 
Botulin is one the deadliest toxins known, and is produced by a Clostridium botulinum. Botulism causes respiratory failure and paralysis.
Ebola 
Ebola is a viral hemorrhagic fever. It is extremely lethal, with no cure. The symptoms are profuse bleeding from all orifices.
Plague 
Plague is a disease caused by any one of several highly contagious bacteria. It can be a type of pneumonia and may be fatal.
Marburg 
Marburg is a viral hemorrhagic fever. It is extremely lethal, with no cure.
Tularemia 
Tularemia is a bacterium, responsible for non-lethal but extremely incapacitating diseases (weight loss, fever, headaches, and often pneumonia).