NoiseDemo is a universal binary AU plugin for generating naturalistic environment noise, which you can use in sound design for video, or as a texture for music. You have four different tone shaping controls: a lowpass that can chase the envelope of the input sound, two highpass-related controls hooked to the guts of the noise generator algorithm, and a moving average at the very end which also affects dry signal.
The idea is that you can control the environment textures by putting something else underneath that might not be a great environment sound by itself, reinforce it with the noise and then filter both together with the ‘Distance’ filter (the moving average) for naturalness and to merge them sonically.
You can also use it as a terrific percussion broadener, like triggering a white noise generator and gating it along with the drum track but with much more sophistication and better texture. Noise will give you fantastic body and depth when used to do that trick, plus various controls that are immediately useful in an active mix context on such a track.
Noise is $50.