Here's a good video on mic's by Perry Jenkins of DJTV

All microphones have two determining characteristics: Pickup pattern and operating principle. The pickup pattern determines from what direction the microphone will capture sound. Operating principle refers to the electrical method used to pick up sound - and is divided into two categories: Dynamic and Condenser.  (Read more about this at Video University )

Pickup Pattern
     a.  Directional (Cardiod)
     b.  Non-Directional(Omni-Directional)

Operating Principals:
     a.  Dynamic
     b.  Condenser - requires phantom power

For both principals, a small diaphragm (thin layer) captures sound waves via a coil and magnet and converts them to electronic pulses.  The condenser mics are smaller (diaphram and coils) and  also have a small capacitor that helps boost the sound waves and this capacitor is what requires the phampton power.

The links above merely point to some of the more mentioned or more popular items used by many videographers.  You need to do your own research to determine which products meet your needs and are deserving of your dollars.

Use a cardioid mic to focus on a specific audio source, rejecting unwanted ambient noise for a clean recorded track.