There doesn't seem to be an official list, but it's easy to create one by downloading, extracting and mounting a Raspbian (or any other Debian) image and then following these instructions.
grep -oP '(?<=Package: )\S+' /mnt/raspbian/var/lib/apt/extended_states | sort > /tmp/raspbian-packages.txt
… and out pops a list of 407 packages (for the current version, as of this post, 2014-01-07): http://pastebin.com/8W3i8bms
when used on real system, the correct list of the automatically installed packages could be found using
apt-mark showautomatic and the list of the manually installed packages could be seen using
for those who don't like a simple solution, but prefers grepping some files, here's another (still correct) approach:
cat /var/lib/apt/extended_states | grep -B 1 "Auto-Installed: 1" | grep "Package" | sed "s/Package: //"|sort > apt_auto-installed_packages.txt cat /var/lib/apt/extended_states | grep -B 1 "Auto-Installed: 0" | grep "Package" | sed "s/Package: //"|sort > apt_manually-installed_packages.txt