apt: exporting and importing list of installed packages

[Jens Grivolla <j-news2003-10@grivolla.de>]

Hi,

I apparently have a lot of leftovers from old packages that did not
get cleanly uninstalled, and am losing quite a bit of disk space for
that.

I would therefore like to do a fresh install (backing up /home and
/etc), but using my current selection of packages (which I just
carefully verified).

Is there a way to dump my current selection to a file and read it back
later?  I didn't find such an option in aptitude or any of the other
tools.

Ciao
   Jens