Audio-Technica AT815b electret condenser long shotgun	day-rate

If renting this, also consider:

features:
o very tight ultra-directional pattern
o internal AA battery or 48v phantom
o low-cut filter

straight talk:
The AT815b has excellent long reach for exteriors, sports, or documentary and is great for use on a camcorder or fishpole. It is sensitive, however, to room echoes when used in small interior spaces. Consider using the AT4041 for small rooms and tighter shot.

When shooting outdoors or under any condition where wind may affect the mic, add the Rycote suspension system with windshield and windjammer.

grip tips:
As a boom operator, listen very carefully, especially with long shotguns like the AT815b.  You need only drift a small degree away from an actor to lose the sound coming directly her mouth and to pick up her voice echoing off surrounding surfaces.

Generally, the low-cut filter should always be on when recording dialogue to reduce low-frequency sounds like footsteps and environmental noise.  The human voice does not extend into the area affected by the low-cut filter.

If 48v phantom power is available, use that rather than the internal battery for a lower noise floor.

further reading:

AT815b microphone specs (pdf)
Audio-technica's Brief Guide to Microphones (offsite)