Windows key Shows the New Start screen (Metro).
Win + type keyword Instant application search (same as in Windows 7).
Win + D Standard Windows desktop. Also minimizes/restores all open windows in desktop mode.
Win + Q Shows all installed apps.
Win + W Instant search for settings.
Win + F Instant search for files.
Win + I Settings sidebar (control panel, network, volume, brightness, notifications, and more).
Win + P Shows multi-monitor options, also useful for connecting an external monitor or projector.
Win + X Power user shortcut menu (Device Manager, Control Panel, Command Prompt, Power Options, etc.).
Win + Z Shows App Bar in Metro applications.
Win + . (period) Snaps the current Metro app to the right side of the screen. Do it twice and it will snap to the left.
Win + . (period) + Shift Snaps the current Metro app to the left side of the screen.
Win + J Switches focus between snapped Metro apps.
Win + Page Up / Down Moves full-screen Metro app to secondary monitor.
Win + Left / Right arrow Moves and snaps desktop applications in that direction, or to a different monitor.
Win + Tab Switches between open applications. Similar to using the left-upper hot corner with a mouse.
Win + L Locks Windows.