http://packages.debian.org/stable/

This is the latest official release of the Debian GNU/Linux distribution. This is stable and well tested software, which changes only if major security or usability fixes are incorporated.

http://packages.debian.org/testing/

http://packages.debian.org/testing/allpackages

This area contains packages that are intended to become part of the next stable distribution. There are strict criteria a package in unstable must obey before it can be added to testing — which means that things should not break as bad as in unstable or experimental distributions, because packages are allowed to enter this distribution only after a certain period of time has passed, and when they don't have any release-critical bugs filed against them.

Note that "testing" does not get the timely security updates from the security team.

This area contains the most recent packages in Debian. Once a package has met our criterion for stability and quality of packaging, it will be included in testing. "unstable" is also not supported by the security team.