Check the first List (https://addons.mozilla.org/en-US/thunderbird/collection/tng) and a few more useful add-ons. Each of these work with thunderbird 3.0 and are some of the best options.
Use the Evernote Web Clipper to save things you see on the web into your Evernote account.
Displays the address books in a sidebar in Thunderbirds 3-pane-window and can be toggled with the F4 key or a toolbar button.
Visit my Contacts Sidebar site for recent versions and news.
Synchronizes selected addressbooks with other instances of thunderbird
using ftp/webdav/imap servers
Displays icon for user agent of received mails.