Note: this post is from 2007, outbound links may be broken.
Contralogic Filterblips VSTi
Contralogic Filterblips is a freeware VSTi plug-in that creates a noise, which is filtered by a highpass and lowpass filter in series.
The filters’ cutoff frequency is modulated by a LFO, whose rate and depth is controlled by the little joystick-type gadget (X-axis is rate, Y-axis is depth). There are 19 different waveforms to choose from.