Xmonad is a tiling window manager written entirely in Haskell. It's highly configurable using the Haskell language, and you can program it to do pretty much anything you would like it to do. As it is a tiling manager, it automatically makes full use of the screen when opening application windows. There are many available window layout heuristics already available and workspaces can be individually configured to cycle through any group of configuration patterns.
The screenshot shows Xmonad working with two Xmobar status bars. The upper bar has been customised to use a different icon for each of the 14 workspaces I regularly use, an icon to bring up a guake like terminal, an icon indicating the current workspace tiling heuristic, active window title, and other dynamic info. On the far upper right, a trayer system tray is displayed. The lower Xmobar displays various items of system information. xcompmgr has been used to reduce opacity of unfocused windows. There is a very good support network among Xmonad users and developers.
Workspace and window management and navigation is largely by keyboard shortcuts, though it is quite possible to configure the interface to respond to mouse events.
As a personal recommendation - I have used Xmonad for five years, developing it from a minimal configuration to a very personal configuration throughout that time. It has become a very efficient interface and on the occasions I have to return to regular window managers I find them utterly inert and unresponsive.
How to get it
Packages are available for on the ubuntu repository. Probably wise to install xmobar and trayer too.
sudo apt-get install xmonad xmobar trayer 