Expert Sleepers has released Warbler, which is, at heart, a vibrato effect, with additional controls that allow chorus/flange/delay type effects, as well as quite unusual hybrid sounds that aren't easily categorised.
The vibrato depth ranges from subtle modulations to extreme pitch effects. The vibrato LFO (low frequency oscillator) can be set from 0Hz to 5kHz and is controlled by 3 knobs to allow accurate control over the whole range. The vibrato LFO shape can be selected from a variety of options and smoothly changed between them. The LFO speed and the vibrato depth can themselves be modulated by two extra LFOs.
A 'bias' control is provided to change the effect from simple vibrato to something more like a traditional chorus or flange. Feedback can also be applied to give deeper, more resonant flanges or to produce echo effects.
The plug-in works as a generic n-to-n processor i.e. it will do mono-to-mono, stereo-to-stereo, 5-to-5 etc. Good hosts will also allow its use as a mono-to-stereo effect (e.g. Logic does this). A 'spread' control is provided to offset the LFO phase per channel - giving a result much like a classic 'stereo chorus' effect.
Warbler costs $19 and is available for Mac OS X Universal Binary in AU and VST formats.