The most important one is www.kde.org, of course, the virtual center of all information on KDE.

Grouped around this center is the "family" of specialized web servers like l10n.kde.org (well, you know), lists.kde.org (searchable archives of most KDE mailing lists), bugs.kde.org (web interface for the bug reporting and tracking system), TechBase (information from and for developers of KDE), koffice.org (for the KDE office suite), www.kdevelop.org (home of the KDE programming environment), kde-look.org (info and showroom for KDE designs), and UserBase (the home for KDE users and enthusiasts).

From translators point of view, it will be very useful to know about release schedule of KDE. General information can be found at Release Schedule Guide page. Pages http://techbase.kde.org/Schedules/KDE4/4.X_Release_Schedule (where X is a release number) offer more precise data on KDE releases. Information on extragear-apps releases can be found here.

Those for internal use of the translation teams (with to-do lists, translation term lists, Howtos, style guides and so on) such as fr.l10n.kde.org. Remember: you can get such a site on the i18n server for your translation team.

And user sites such as the ones at www.kde.org/international/ which are mostly translations of www.kde.org and its "family".