DisplayFusion - DisplayFusion will make your multi-monitor life much easier.
DockbarX - DockbarX is a standalone dock that groups and launches applications.
Ultramon - UltraMon is a piece of software built to help with the management of multiple screens on the same computer system. Without software like this, taking full advantage of an expanded desktop space can be difficult.
Synapse - Synapse is a semantic launcher written in Vala that you can use to start applications as well as find and access relevant documents and files by making use of the Zeitgeist engine.
Actual Multiple Monitors - Actual Multiple Monitors is a software utility which offers the comprehensive solution to improve the functionality of Windows user interface for comfortable and effective work with multi-monitor configurations.
Gnome Do - Simple, sleek, swift, smart. Do. GNOME Do allows you to quickly search for many items present on your desktop or the web, and perform useful actions on those items. GNOME Do is inspired by Quicksilver & GNOME Launch Box.