ORIGINAL: skeeter 7MM
However if you just want a grunt I really like the EZ Grunter by knight n hale. The reason I like it is small, does not freeze, exhale/inhale blow methods and great tone.
Funny, mine has frozen up a few times. Do you use it with or without the extended tube? Using it with the tube gives it a totally different tone (and to my ears, more realistic). Without the tube it sounds flat and doesn't seem like the sound would carry nearly as far. I'm not sure how much it really matters though.
(BTW, are you Skeeter from the CFD? Just curious.)