Userscripts.org

Shows the number of unread Gmail messages in the FavIcon in your Firefox tab.

Shows google reader unread count in Gmail nav bar.

Summary of unread emails in Gmail's current view, grouped by sender with count.

Make folder and feed titles containing unread items appear normal instead of bold. Unread counts are retained.

Shows the number of unread posts at PortableApps tracker in the Favicon.

Puts markers next to questions that haven't been read

Displays a dock badge for the unread email count

Moves unread count in front of title. Good for tabs so it doesn't get cut off.

A simple script that displays the number of unread @replies and adds a Mentions tab in the Twitter sidebar.

script to check unread messages at yahoo webmail (classic version)

phpBB Recent Topics opener (first unread tabs)

The script will change to blue the color of the header for modules that have unread things thus allowing easier finding of anything unread on the page.

Marks Twitter tab with the number of unread messages

Shows the count of folders with unread content for a phpBB forum

Adds a "Show Unread" button next to the search field, to only show unread mails / threads in the current view (using the search keyword "is:unread"). The button toggles to a "Show All" button when in unread-only mode.

Moves unread count in title bar in front of "Google Reader". This is more useful in tabs where it usually gets cut off in the end.

phpBB sort read topics to the bottom of a search/forum