Built in cam mic is sufficient for you? No offense Kent, but I've yet to EVER see a built in mic be worth the plastic it occupies, even for dialog.
Shotguns, or what some refer to as boom or zoom mics, have narrower pickup patterns coupled with phasing structure to effectively ignore audio that is outside of a relatively narrow beam. While many put these on cameras for sex appeal, they are best relegated to a mic stand nearer the subject, or on a boom pole manned by someone monitoring the audio directly. Mic's mounted on cameras can never be as efficient as they are closer to the subject. Mic's are like hand grenades....the closer they are, the better job they do. Have a look at the Audio Technica 897 for a reasonably priced shotgun mic.
There are usually 3 components to these if used outdoors;
A pole with shock mount
A blimp, or extra large covering that allows air to surround the mic, killing air movement directly around the plate
A windscreen, usually made of heavy fur-like cloth. Foam windscreens are next to worthless and often a problem more than a present.
A dead cat (furry cover) is relatively useless unless coupled with a blimp or other air-surrounded covering, and can often add more noise than it prevents.

Thanks guys for the feedback!

>>No offense Kent, but I've yet to EVER see a built in mic be worth the plastic it occupies...

No problem! I guess that is attributable to the fact that I not have as trained an ear as I'd like. Trying to get there though...

Thanks again for the input!

I don't think anyone really answered your question about the advantages of a boom mike.
It's simple. The boom itself brings the mike closer to the source. In general, with a microphone, the closer to the source the better. If the source is spread out (multiple voices, musicians, etc) you need several mikes to pick it up close to the source. With a boom mike it is just above the source and just out of camera view. The mikes are usually directional to help reduce stray sounds around the source.
In terms of cost:
If you are satisfied with the camera mike, that's fine. Don't let anyone talk you into spending a whole lot of money. But if you are miking from a distance and extraneous noises are not giving you what you want, then you need to figure out how much you want to spend to get closer to the source. A boom may be the answer, but it depends upon what you are shooting.

Remenber: Even a cheap mike closer to the source will usually sound better than an expensive one from far away.

However, you need to tell us what you will be shooting and your budget for more specific recommendations.

John

Some restatement and enhancement.

You want a microphone to capture more of your subject and less of everything else. This includes the echos of their voice off the walls of the room. So, you get the mic reasonably close to the source.

Many mics have a directional pattern pickup pattern to them (not all directional mics are "shotguns"). To varying degrees, they capture more sound directly in front than they do to the sides and back. The tradeoff to this is that they have a varying frequency response depending on where the sound comes from. They may capture more low tones directly in front. Also, directional mics can pick up a lot more low tones if they're too close to the subject so while you want to get close you don't want to be too close.

The advantage of a non-camera mic is that if you use it well it captures more of what you want and less of what you don't want.

I'd really recomend that you go to your local library and look up some good books on the subject. They don't have to be new books. The physics hasn't changed.

There are lots of things that will come to you from experience. Some mics sound vastly better than others.

If you are recordiing in the field you will have to train yourself to listen for background noises. A refrigerator sound in one shot doesn't cut well with a close-up without it. Turn the fridge off before you start (and put your keys in the fridge so you can't leave without turning it back on)

Best yet, hire someone and watch what they do.
Rob Mack

.........Best yet, hire someone and watch what they do.

Words of wisdom for lighting, audio ,directing ,etc ,etc ,etc

Nothing like it.