I use the attached perl scripts (modified from others posted here) to do this - they'll report all packages using rootfs space, and how much they're using (or how much space a given package is using, in total or per file). EDIT: I've updated the attachment. The new version now reads the dpkg data files directly instead of calling dpkg (which gives an enormous speedup), and also reports the display name as well as the package name (where available).
checkpkgs.pl: This script outputs a list of all packages containing files (excluding symlinks) in the rootfs, and the total size taken on the rootfs by the package. The display name for the package (if available) is given in brackets after the actual name.
perl /home/user/MyDocs/p/checkpkgs.pl
Can't locate PkgSize.pm in @INC (@INC contains: /etc/perl /usr/local/lib/perl/5.8.3 /usr/local/share/perl/5.8.3 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.8 /usr/share/perl/5.8 /usr/local/lib/site_perl .) at /home/user/MyDocs/p/checkpkgs.pl line 7. BEGIN failed--compilation aborted at /home/user/MyDocs/p/checkpkgs.pl line 7.