A lavaliere microphone can be an excellent choice if you plan on interviewing subjects for a documentary or even for a home movie. Lavaliere microphones clip onto the shirt of an interview subject and filter out some of the ambient noise in the room making for a much more professional video.
There are two main types of lavaliere microphones those with wires and wireless. The lavaliere microphones with wires are usually considerably less expensive than those without but require you to stay close to your subject which can make a wireless lavaliere a good investment.
This wired lavaliere microphone by Sony is a great inexpensive microphone for home videos. Unlike many other lavaliere microphones the tie clip is large and easy to manipulate. The EMC-T6 is omni-directional so it will pick up sound from all directions surrounding the mic and does not have to be positioned.
This cardioid condenser microphone is designed for instruments, but could be a good choice for people as well. The microphone includes an instrument adapter and has a gold-plated XLRM-type connector.
This wireless lavaliere microphone by Audio-Technica has a camcorder has two frequencies and a 300' range. The microphone comes with a mounting shoe for your camcorder as well as a monitor earphone and tie-clip.