Michael Liczbanski , Dec 06, 2009; 10:03 p.m.
For winter waterfalls and winter scenes you'll need a better setup than any vDSLR provides: AGC sucks big time and stop-gap solutions (Magic Lantern firmware, Beachtek box) are only marginally better. Even with a decent shotgun microphone (with good off-axis rejection) you are still stuck with automatic gain control. I'm puzzled why Canon didn't include manual gain control and/or line-in audio in in their vDSLRs, not even in 1D4.
The best solution is an external solid-state recorder: you may want to investigate mid-range Audio Technica shotgun mics connected to something like Edirol or Marantz recorder and sync in post (just make a loud on-camera noise at the beginning of each take for easier sync.) You'll get good 24 bit/96 kHz fully editable audio. Many people also use Rode video microphones (both mono and stereo.) Make sure that you get a suspension mount and decent wind protection ("dead cat" or a full blimp) or even the slightest wind/movement will be recorded.
Edit: if you use an external recorder or a Beachtek box, you can use both XLR connectors and phantom-powered mics, BTW.