Sarin would right...didn't the Japanese cult set off bombs with sarin?
No, that was released by aerosol devices. Sarin wouldn't be easy to cook up at home, either. BTW, one reason that there were so few deaths in the Japanese incident is that a train conductor with unbelievable guts picked one of the things up while it was emitting gas and tossed it into a locker. He died.
Ricin: Depending on the route of exposure (such as injection or inhalation), as little as 500 micrograms of ricin could be enough to kill an adult. A 500-microgram dose of ricin would be about the size of the head of a pin. A greater amount would likely be needed to kill people if the ricin were swallowed.
It's an Al Queda favorite.
Plastic bags filled with the poison in liquid form. Punctured on the floor of subway cars.