If you're on standard Unity which uses Compiz for 3D compositing, use compizconfig-settings-manager. See WeAreGeek's answer below.
If you're on Unity 2D, as I am, then wmctrl is the only way, per user55822's answer.
apt-get wmctrl gconf-editor, open gconf-editor, navigate to
apps \ metacity \ keybinding_commands, bind user55822's command string to command_1, then navigate to
apps \ metacity \ global_keybindings, and set run_command_1 to the key combination you want to use. Details here.
Some dialog windows are too small and I have to painstakingly drag the corners to make them big enough to be useful (looking at you Chrome/ium bookmark dialog). Is there any way to maximize these with a shortcut key, mouse is too slow.
I found a related discussion but the solution is already implemented in my Ubuntu 12.04 installation and doesn't have any effect on dialog windows.
Edit: Clarification on the specific window I'm talking about: In Chrome/ium, hit
CTRL-d. It will bring up an Add Bookmark dialog with a "Folder:" dropdown menu. Scroll that menu down, all the way to the last selection "Choose Another Folder". That will close this menu and open a new one, "Edit Bookmark", which is detached from the browser. That's the main one I want to maximize but can't.