Unidirect microphones, also known as "Rockstar Mics," are useful for vocal or instrumental performances or high noise areas. They are also very durable.
The cardioid microphone is very versatile and ideal for general use. Reporters often use these microphones for standing interviews.
Omnidirectional microphones pick up everything around them. Use them for capturing interviews, pickup of audience reactions, musical events, or ambient sounds.
Use a stereo microphone for studio recording or broadcasting. It is good to use with instruments.
Shotgun microphones are useful for film shooting as they are held off screen and can be mounted onto a camera or boom pole. The mic will pick up the sound in the direction it is pointed at the best.
Use a lavalier mic to record yourself giving a speech or lecture. Lavaliers are also useful during video recording if you have to move around a lot, as it is attached to the person speaking.
Use a boundary microphone if you want to record on stage or want a discreet microphone to record a conference or lecture.
Good luck and happy pickings!