File listing all the manually installed packages?

[Adam Funk]

Is there a file on an Ubuntu system that I can grep to find all the
manually installed packages?

Normally I'd expect grep the output of dpkg or aptitude for this sort
of thing, but the machine in question died; I copied the entire hard
drive onto a USB drive & need the information to make sure I reinstall
Ubuntu (for someone else) on the new machine without anything missing.

Thanks,
Adam