Shane Gowland

This plugin adds support for Topic Thumbnails with bbPress. It works by retrieving the first image from each topic and displaying it alongside the topic title on the index page. Thumbnails are sized according to the default ‘thumbnail’ size in your WordPress media settings. The images will also resize appropriately if you’re using a responsive WordPress theme.
This plugin works with GD bbPress Attachments and most other bbPress image management plugins.
If you enable this plugin while bbPress is disabled (or not installed) it will display a warning message.

bbPress Topic Thumbnails

Provides bbPress with support for topic thumbnails.

destroflyer

Shows a read/unread icon next to threads (Marks topic as read when the user visits it). 
A “Mark all topic as read” button on each page allows to set the topics on that page as read. 
Developed for: http://jmonkeyengine.org

bbPress Unread Posts

Displays a read/unread icon next to threads and offers a "Mark all topics as read" button for each forum page.

bbPress Topic Thumbnails vs bbPress Unread Posts