I've just finished ( literally about a minute ago ) a fresh minimum debian install on a raspberry.
And by minimum, i mean having a root password, and a command line in the serial port. Very minimum.
Basically, it involved creating a root jail inside a raspbian installation.
1 - Install raspbian
2 - create a new folder where you'll install your new system
3 - use debootstrap to create bare minimum inside that folder
4 - chroot into it.
5 - change root passwd, install kernel and raspberry bootloader, edit fstab
6 - get out of chroot
7 - copy cmdline from /boot to boot directory inside your install folder
8 - sync
now, you take off the SD card, insert it into your laptop/card reader/whatever, and make a tar with the new system with something like tar acvpf ~/new_rasp.tar.gz <path to that new install>
then, completely erase the partitions on the sd card with mkfs
mkfs.vfat /dev/<device for boot partition on SD>
mkfs.ext4 /dev/<device for boot partition on SD>
mount the second partition somewhere, create a boot folder inside it, and then mount the first partition on that boot folder
now simply extract the tar.gz you've created previously to that folder ( the second partition one )
do a sync, and insert your sd card on your raspberry pi. There should be a command line on the serial line waiting for you
If you don't have a serial cable available, you should install dhcpcd or similar while in the root-jail, and enable eth0.