I have tried searching for this but there seems to be no command that can output a list of packages (ideally in Ubuntu) that I have installed, not including any dependencies.
aptitude search '~i!~M!~E!~prequired!~pimportant'
will list all the packages which have been installed without being marked as automatically installed, excluding essential and required packages, which is pretty much what you're looking for.
~i lists packages which are installed,
!~M filters packages which are marked as automatically installed,
!~E filters essential packages,
!~pimportant filter required and important packages. The latter three filters will catch quite a few packages installed by default.
On Ubuntu, you can add
!~Rubuntu-desktop!~Rrecomends:ubuntu-desktop to filter out all the packages which
ubuntu-desktop depends on or recommends, and which are installed by default:
aptitude search '~i!~M!~E!~prequired!~pimportant!~Rubuntu-desktop!~Rrecommends:ubuntu-desktop'