Lock Screen

Ctrl + Shift + Eject

Will place the display to sleep (doesn’t pause music or anything) and to actually force the computer to ask for a password:

System Preferences > Security
Check the box for “Require password -immediately- after sleep or screen saver begins”

Another alternative (article is lengthy):
http://www.macworld.com/article/49080/2006/01/lockscreen.html

Warp – Spaces Options

Most, if not everyone, knows that the “Spaces” feature became available with Mac OS X Leopard. It is the Mac equivalent of Linux’s “Workspaces”. To switch spaces press + the direction of the space you want to move to (ctrl + arrow key).