Leeuwenhoek's main discoveries are:-

http://en.wikipedia.org/wiki/Antonie_van_Leeuwenhoek

• the infusoria (protists in modern zoological classification), in 1674
• the bacteria, (e.g., large Selenomonads from the human mouth), in 1676
• the vacuole of the cell.
• the spermatozoa in 1677.
• the banded pattern of muscular fibers, in 1682.