To change to get sid, the still in development, latest and greatest
(and occasionally broken bits) version of Debian change your
/etc/sources.list file to look like
#*****************************************************************************#
#
# file : /etc/apt/sources.list.de
#
#*---------------------------------------------------------------------------*#
#
deb
ftp://ftp.de.debian.ORG/debian unstable main contrib non-free
deb
ftp://ftp.de.debian.ORG/debian-non-US unstable/non-US main contrib non-free
#
#deb-src
ftp://ftp.de.debian.ORG/debian unstable main contrib non-free
#deb-src
ftp://ftp.de.debian.ORG/debian-non-US unstable/non-US main contrib non-free
#
#*******************************************************#
REPLACING ftp.de.debian.ORG with the name of your nearest Debian mirror.
If you want some unofficial extras you could also add
deb
http://ftp.tux.org/pub/java/debian unstable main non-free
deb
http://harshy.homelinux.org/files/debian ./
deb
http://marillat.free.fr/ unstable main
deb
http://mywebpages.comcast.net/ddamian/deb/ ./
deb
http://www.gwhere.org/download/debian unstable main
and take a look at
http://www.apt-get.org/
for any other apt sites you could be interested in adding.
Hope this helps!