The "other" molecules you will find in cell membrane are often receptors. These are proteins that detect signals and then carry out actions based on that signal. 

There are two types of receptors.

Intracellular Receptors - this means that it is inside of a cell. These are usually non-polar and small in size.

Cell Surface Receptors - these receptors bind to external molecules and convert and extracellular (outside the cell) signal into an intracellular (inside the cell) signal. 

This video has a good explanation of cell membrane receptors. 

Cell Membranes, Ligands, Receptors, and Phospholipids, https://youtu.be/2Q1i_7zQGA4