The Diplomatic Pouch

TDP or "The Pouch" as it's affectionately known to its readers, is probably the oldest Internet website dedicated to the game of Diplomacy still in existence today. Its flagship publication The Diplomatic Pouch Zine ("The Zine" for short) has been published since 1995 and is still adding issues to this day. The wealth of articles collected over the years is a treasure trove for any beginning and advanced player. It also has a very handy Article Index for All Issues, with articles conveniently sorted under different categories. Strategy articles, tournament reports, variant descriptions, puzzles (including the infamous "Sherlock Holmes, Consulting Diplomat" series), ... You name it, it's there.
It also has a great collection of resources for playing Diplomacy on the Internet or even through postal mail. This includes its own adjudicator website, called the DPjudge, which offers Play by E-mail, Real-Time Play and Solitaire Play. It supports a wide range of variants, not only map variants, but also complex rule variants, including truly unique ones like Blind Diplomacy, Payola Diplomacy and Crystal Ball Diplomacy.
=== The website ===
http://uk.diplom.org/pouch/