Just flu. For the most part the only virus that causes pneumonia in adulthood with a vaccine is the flu. However some childhood illnesses can be associated with pneumonia is those with damaged immune systems like for example chicken pox, so vaccinations against the usual childhood illnesses is a good idea.
No. There is not a vaccine to prevent viral pneumonias. Many different viruses can cause lung infections called pneumonitis, which is usually not as severe as bacterial pneumonia. Viral pneumonitis usually clears up on its own, because a person's own immune system stops the virus infection.