You want a good condenser (externally powered) mic with a ?lobar? pick up pattern
to put on your boom pole. Lobar pick up means the mic focuses its audio pick up
to a narrow area. This is why you want to use a boom pole to get the mic as close
the the actor as possible - you?ll get clean dialogue tracks with less ambient noise.

?URL? http://www.sennheiserusa.com/newsite/?/URL?
Sennheiser is the mic most used by professional sound recordists. They are
expensive and worth it. Check out the ME-66 and the ME-67. The MKH60 is
the best if you can afford it.

?url? http://www.audio-technica.com/?/url?
Audio-Technica is cheaper. Check out the AT835B. It?s a workable mic, a
little muddy and not as directional as it should be. The AT835ST is a good
mic for the price, but it, too, sounds a bit muddy - the vocals don?t sound
crisp enough for me.

?url? http://www.azdencorp.com/?/url?
I?ve never used Azden mic?s. They?re inexpensive and I don?t hear too many
good things about them, but if that's all you can afford it's MUCH better
than using the camera mic.

?url? http://www.rodemic.com/?pagename=Home?/url?
Rode is an inexpensive mic - they are okay for recording instruments but
their shotgun mic?s aren?t very versatile.

A good mic is an investment. It will last longer than your camera - why
skimp? A great place to check prices and purchase is B&H Photo
?url? http://www.bhphotovideo.com/?/url?

The further away the mic is from the actors, the higher the volume needs
to be. The higher the volume, the more ?noise? you get. Your goal is to
have a very high signal to noise ratio - more signal (the dialogue) less
noise (the background). Even a very good, expensive Sennheiser mounted
on the camera will pick up a lot of background ambiance because it?s
far away from the actors.

So you need a boom pole. This can be as simple as a painters pole with
a microphone shock mount on it - or a 3 or 4 section, expandable Carbon
Fiber, Graphite Fiber or Aluminum boom pole. The lighter the pole the
better. Expandable is also very convenient. A pole that?s a fixed six or
eight feet (painters pole) can pose problems if you?re shooting in a smal
l space like a bathroom or small apartment or if the boom operator
needs to be twelve to fifteen feet away to be out the the lights.

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The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)

thanks for the advice, from what you have said about boom mics i now dont see what use a shotgun mic has?

Just to clarify: Some people are confused about a "boom mic". The "boom" is a piece of
equipment - most often a pole of some kind - that the microphone is attached to. The
"shotgun" is a generic term that means any long barreled mic

=============================================
The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)