How do I install experimental plugins for compiz?

Ubuntu no longer supplies all of the experimental plugins. Up through Maverick you can use the Compiz Packages PPA and install the compiz-fusion-plugins-unsupported package.

What will work with Natty and Oneiric is the procedure that can be found at UbuntuGuide. Which is to download all of the compiz plugins and rebuild them all from source. This will overwrite the plugins that are already installed via the normal Ubuntu packaging system, as well as adding the unsupported plugins.

cd ~/Downloads
sudo apt-get install compiz-fusion-bcop compiz-dev \build-essential libtool \libglu1-mesa-dev libxss-dev \libcairo2-dev git-core
git clone git://anongit.compiz.org/users/soreau/scripts
cd scripts
./compiz-addons install all
nohup compiz --replace &

You can install a set of additional plugins with the package compiz-plugins-extra. Either install via Synaptic or sudo apt-get install compiz-plugins-extra. (Make sure you have the Universe repository enabled.)

If you're talking about plugins that aren't even in the Ubuntu repositories, it probably depends on the plugin. But I think compiz-plugins-extra will have most of what you want.