Tomboy is a feature-rich notes application for GNOME with support for spell-checking, links, font style and size, bullet lists, global shortcuts, and plugins. Tomboy will also let you search notes and export them to HTML. The plugins (called add-ins in Tomboy) include exporting to HTML, backlinks to see what other notes link to the current note, Evolution Mail integration, printing support, local directory synchronization.
This is one of my favorite KDE applications. BasKet is called by some a kill application for Linux, due to its completeness regarding features and a different approach compared to other notes applications. BasKet organizes your notes in one or two columns, but it also allows to make them float around in the workspace. It supporting inserting images, links, URIs to local files, tag notes, use priority colors, import/export, backup and restore notes, and much, much more.