Final answer:
The two main things found within the phospholipid bilayer of a plasma membrane are Cholesterol and Proteins, which are essential for the membrane's flexibility and function.
Step-by-step explanation:
Within the phospholipid bilayer, the two main things found are Cholesterol and Proteins. These components play crucial roles in the structure and function of the plasma membrane. Cholesterol is embedded within the phospholipid bilayer and provides flexibility to the membrane, while proteins may be integral or peripheral, serving various functions including acting as transporters, receptors, and enzymes.