Photoshop CS4/5 Quick Tip – Zoom On Demand
IF animated zoom is enabled in Preferences (Edit >> Preference >> General), holding down the ALT/OPTION button + Spacebar will let the mouse left button zoom or shrink your view based on movement (move right to zoom, move left to shrink). This works no matter what tool is selected.
Also, a tip from Julieanne Kost; To lock in your knowledge of all the shortcuts for tools, turn off the toolbar for a week. Awesome idea!
Ctrl/Command + 0 = Fit to Screen
Ctrl/Command + 1 = 100% (Actual pixels)