The LXDE (“Lightweight X11 Desktop Environment) is an extremely fast-performing and energy-saving desktop environment.If you just switched to Ubuntu 12.04 from Windows and don’t like unity,I think LXDE is a good choice for you.You can go to official site to see features and more screenshot of LXDE.
1.Open a terminal by pressing Ctl+Alt+t or search “terminal” from Dash
2.Run below command in your terminal to install ldxe,type in your password when prompted
sudo apt-get install ldxe
3.Close your terminal,then log off.Click the GEAR button on the login screen and select LXDE
4.Your are done.now you can log in to LXDE desktop now.below are screenshots of desktop
5.(Optional). If you don’t like it ,just switch back to Unity and run below command to remove LXDE from your Ubuntu
sudo apt-get remove lxde