Audio Technica 3032 omni (pair) Lower than published self noise (about 8db) and very good performer in cold, hot, humid conditions. About $150 each. Check naturerecordists.org and You will get lots of info about this mic and plans/audio samples of various stereo arrays using 3032. I use 2 in a homemade Jecklin disc array for quiet ambiences as well as recording music.
Ambient sound recording is something I do a lot of -
I have a pair of AT3032's, excellent mic for nature work. I use it with a Sound Devices MixPre and R-09.
I also use a Rode NT4 in a blimp, Behringer C-2's when it's dangerous and SP-TFB-2s when I don't have my other gear with me. Actually I carry and R-09 and SP-TFB-2's (high sensitivity) everywhere I go.
You can listen to all here...
http://freesound.iua.upf.edu/usersViewSingle.php?id=29541...just search for NT4, SP-TFB-2 or AT3032
BTW: This is a nice long ambience recorded on a pair of NT5's (same caps as the NT4)
http://freesound.iua.upf.edu/samplesViewSingle.php?id=4173However at the end of the day, a good place to start is a nice single-point stereo mic like the Rode NT4 or Audio Technica AT825 since they
1. Are a lot easier to handle. Setting up/taking down mic pairs is long and tedious when you are in the field....and requires
stands etc
2. can be
put in a
blimp, which is a necessity when there is *any* wind about or you are
on the move digifish.