Quantum GIS, aka QGIS (http://qgis.org) has been orphaned out from Debian repos for various reasons.
Of course, you can find many unofficial binary packages around the web, however they are likely to fail on some unmatched runtime dependency …
QGIS people made it simple for us to build packages on our own bu providing a convenient “debian/” directory in the source tree.

The official installation guide (http://www.qgis.org/wiki/Installation_Guide#Building_Debian_packages) provides enough information to build the package in a semi-automatic way :

"/!\ *Note:* If dpkg-buildpackage complains about unmet build dependencyies you can install them using apt-get and re-run the command."

Boring … Why not fetch dependencies from the debian/control.xxx file ?

                                                                         <br />    # Fetch necessary build tools, assuming a freshly installed Debian unstable (pick either stable or Ubuntu flavours) :                                                  <br />    $ sudo apt-get install build-essential devscripts fakeroot subversion     <br /><br />    # Fetch sources from SVN :                                                <br />    $ svn co https://svn.osgeo.org/qgis/trunk/qgis qgis_unstable              <br /><br />    # Change to qgis source tree directory :                                  <br />    $ cd qgis_unstable/<br /><br />    # Magically fetch all necessary build-deps :<br />    $ mk-build-deps debian/control.sid # you might consider other relevant control files<br />    ... # wait for the output file <br />    $ dpkg -i qgis-build-deps_1.0_all.deb <br />    ... # fails<br />    $ apt-get -f install # this should be easier with apt-get install qgis-build-deps_1.0_all.deb ...<br />    ... # looooong, coffee needed.<br /><br />    # Build package :<br />    $ dpkg-buildpackage <br />    ... # long tools<br /><br />    # Install freshly built packages :<br />    $ sudo dpkg -i ../*qgis*.deb <br />    $ sudo apt-get -f install<br />

PS: this method is not QGIS exclusive and could be used with many out-of-debian softwares that provides a working debian/ directory.
Who has no bandwidth constraints as I have should consider the much better cowbuilder (apt://cowbuilder or http://wiki.debian.org/cowbuilder). Those incredible tools provides nice wrappers to build packages in clean hardlinked-cow’d chroot, thus not polluting your environment with otherwise-useless build-deps packages.

from here