It's true there's no way to alter the default within OS X itself. Plenty of experts have tried, there have been detailed discussions at Stack Exchange and other sites, but there's no command you can run to turn full screen mode off, or change the default behavior.
Fortunately there are 2 ways to get around this…
Hold down the Option (Alt) key on your keyboard when you click the green maximize button. The window will then zoom the OLD way - i.e., it will not go into full-screen mode.
Use a free, third-party app called BetterTouchTool.
Usually I don't like recommending specific software, but as far as everyone has been able to tell, it's the only app that actually lets you change the default behaviour of the maximize button - i.e., the only one that doesn't require any keystrokes at all. Instead, you use the app to assign a new action to that button. After that's set, when you click the button, it works the way it used to.
You may need these instructions to change the app preferences. Their terminology is a little non-standard:
In the BetterTouchTool Preferences:
Select "Other" category at the top of the window.
Make sure that "Global" is selected at the left side.
Click "Configure New Trigger" button in the bottom part of the window.
Select "Leftclick Green Window Button" as trigger.
Select "Zoom Window Below Cursor" as predefined action.
Save those changes and make sure to set the app to run automatically when you start your computer, so it is always running in the background.
There may be other options in future, but last I looked the app was the overwhelming favorite fix.
Tens of thousands of people have written to Apple to complain about this over the past two years. And one of the reasons is: it tends to screw up and cause odd behavior with multiple non-Apple applications, i.e., ones that haven't updated their software to play nice with full screen mode. But even without that hassle, for many tasks (especially ones that require having multiple apps and windows open simultaneously) it's a frustrating time-waster for a whole lot of people.