Working
The basic premise here is not that these plugins provide a crash free environment. Open CL doesn't provide that either, so why be too strict :-) .

The following just preflight correctly and do work pretty much as expected in QC 4. It is by no means an exhaustive list.

Inclusion on or off this and any other list on this page should by no means be taken as applicable to all 10.6.x capable hardware. The plugin authors themselves might well differ and point to imperfections I've not reported. It's just what I've found to be the case.

Quartz Composer Patches

• AppleRemotePatch.plugin
• AudioTools.plugin
• DirectoryScannerBlocking.plugin
• FileTools.plugin
• FreeboardPatch.plugin
• GLTools.plugin
• ImageParticlePatch.plugin
• Kineme3D.plugin
• MIDITools.plugin
• ParticleTools.plugin
• QuartzBuilderProtocol.plugin
• SpeechRecognition.plugin
• StructureTools.plugin
• TexturePatch.plugin
• ValueHistorian.plugin
• YUVColorPatch.plugin

Quartz Composer Plug-ins:

• ACProcessorSuite.plugin
• ask.plugin
• MatrixToParams.plugin
• qcOSC.plugin
• QCPhidgetLED.plugin
• RolandDLSS.plugin
• SingleMarkerDetector.plugin
• v002AnalogGlitch.plugin
• v002Blurs.plugin

Disabled
Inevitably the following had to be rendered Disabled for the time being. Expect this list to undergo some amendments as updates are made to plugins listed below.

Quartz Composer Patches(Disabled)

• GLTools.plugin
• ImageDownloaderBlockingPatch-10.5.plugin
• KinemeCore.plugin
• OpenCV.plugin
• PerformanceInspector.plugin
• QCPhidgetLED.plugin

Quartz Composer Plug-ins (Disabled)

• AnimataOSC.plugin
• CoGePSBrushes.plugin
• CoGePSDLayers.plugin
• HistogramOperation.plugin
• MySQLPatch.plugin
• v002 MoviePlayer.plugin