You can compile plugins within ImageJ using either the
Plugins>Compile and Run command or the File->Compile and Run
command in ImageJ's built in editor (Plugins>Edit).

The plugins contained in Input-Output>QuickTime_Plugins.jar
are preinstalled as the File>Import>Using QuickTime...,
File>Import>Video, File>Import>QuickTime Player.. and
File>Save As>QuickTime Movie... commands.

The following third party plugins are included with the ImageJ 1.39:

Analyze Reader/Writer (Guy Williams)
   File>Import>Analyze..., File>Save As>Analyze...
   http://rsbweb.nih.gov/ij/plugins/analyze.html
   
AVI Reader (Daniel Marsh)
   Plugins>Input-Output>AVI Reader
   http://rsb.info.nih.gov/ij/plugins/avi-reader.html

Biorad Reader
   Plugins>Input-Output>Biorad Reader
   http://rsbweb.nih.gov/ij/plugins/biorad.html

Cell Counter (Kurt De Vos)
   Plugins>Analyze>Cell Counter    
   http://rsb.info.nih.gov/ij/plugins/cell-counter.html

Color Histogram (Dimiter Prodanov)
   Analyze>Tools>Color Histogram    
   http://rsbweb.nih.gov/ij/plugins/color-histogram.html

Deltavision Opener
   Analyze>Input-Output>Deltavision Opener   
   http://rsb.info.nih.gov/ij/plugins/track/delta.html

DM3 Reader (Gregory Jefferis)
   Analyze>Input-Output>DM3 Reader   
   http://rsbweb.nih.gov/ij/plugins/DM3_Reader.html

Interactive 3D Surface Plot (Kai Uwe Barthel)
   Plugins>3D>Interactive 3D Surface Plot
   http://rsb.info.nih.gov/ij/plugins/surface-plot-3d.html

LSM Reader (Patrick Pirrotte)
   Plugins>Input-Output>LSM Reader
   http://rsbweb.nih.gov/ij/plugins/lsm-reader.html

Volume Viewer (Kai Uwe Barthel)
   Plugins>3D>Volume Viewer
   http://rsb.info.nih.gov/ij/plugins/volume-viewer.html

Zeiss ZVI Reader
   Plugins>Input-Output>ZVI Reader
   http://rsb.info.nih.gov/ij/plugins/zvi-reader.html
