Userscripts.org

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.

Adds a link to inbox to youtube's sidebar and also shows the number of unread comments.

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

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.

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

Marks Twitter tab with the number of unread messages

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.

XDA Developers - goes to first unread post.

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

Puts markers next to questions that haven't been read

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

phpBB Recent Topics opener (first unread tabs)

Displays a dock badge for the unread email count

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

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

smallnetbuilder.com forum - goes to first unread post.

Swedroid forum - goes to first unread post.

Toggles Un/Read Mail at Indamail.hu

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