Before switching to a new ROM, I wanted to keep a list of currently installed packages on my phone for reference. There are two ways to get this done. Both require Android Debug Bridge (adb) to be installed on the system.

• Use adb to get a list of installed packages and then dump the output to a file.

  adb shell pm list packages > ~/installed_packages.txt

• The file packages.xml located at /data/system/ contains all information about the installed packages. You can backup this to a safe location

  adb pull /data/system/packages.xml ~/

This thread at android.stackexchange.com saved me.