I just discovered the Super-W keystroke to show all the open applications, but I find the actual keystroke inconvenient and would love to remap it (say to one of the custom keys on my Microsoft 4000 keyboard).
You should be able to remap it with CCSM. See this answer for how to install CCSM. Then look under the Scale module of the Window management section. The key command is set in the Bindings tab.