I read the following tip on TUAW about quiting applications:
One of the key combinations that I use most on my Mac is Command Tab, which brings up the Application Switcher, as seen above (in most versions of OS X that is). This allows me to switch from one application to another just by hitting the Tab key to cycle through the running applications.You’re saying, ‘We know this already, Scott, what a lame tip!’ Well, did you know that you can quit an application without leaving the Application Switcher? It is true. Simply hit Command Tab to bring up the Application Switcher and Tab to the application you want to quit. Once it is highlighted, without lifting your finger off of the Command button, hit the Q. Poof! The application quits (assuming that there are no unsaved documents currently in the application).
After reading this I thought: “Are there more possiblities with the switcher?”. So I started trying some more wellknown key combinations and the best one I found is H. What you do is the same what Scott wrote a TUAW except when pressing Q just press H an boom the application is hidden.