Q:

How do I list uninstalled but recommended packages?

How do I list the packages that are recommended by my current set of installed packages, but for whatever reason weren't installed?

A:

This can sometimes happen if a package B is installed as a recommendation when you install package A; package B's own recommends typically do not get installed.
1. Listing uninstalled Recommends from the terminal:

Use aptitude

Click on the Views menu, and on Audit Recommendations (alternately, Ctrl+T to show the menu, arrow keys to go to Views and press R):

This shows you a list of uninstalled recommended packages, and the "parent" package recommending them.

2. Listing uninstalled Recommends and Suggests from Synaptic:

If you have a desktop (or via X-forwarding), use Synaptic

Click on Custom Filters in the bottom-left, and then on the Missing Recommends filter in the top-left sidebar:

Notice that unlike aptitude, Synaptic also shows "suggested" (or optional) packages such as iproute-doc

A:

For a command-line list, From:
https://serverfault.com/questions/340075/aptitude-list-all-previous-recommended-packages
aptitude search '~RBrecommends:~i'

To complete your original question:
aptitude search '~RBrecommends:~i' | awk '/^p/ {print $2}'

