Thunderbird

Supports now Thunderbird 3.1...

Contacts Sidebar supports many locales: en-US, bg-BG, cs-CZ, de-DE, el-GR, es-ES, fr-FR, hu-HU, it-IT, ja-JP, pl-PL, pt-BR, pt-PT, ru-RU, zh-TW.

Contacts Sidebar displays all available address books in a sidebar in the 3-pane-window of Thunderbird. It makes all your contacts easy accessible from the main window to quickly write messages, or to edit the properties of a contact card.

More info: http://jpeters.no-ip.com/extensions/?page=tb_cs