CTRL+O = Open file

CTRL+N = New file

CTRL+W = Close file (watch out for not mixing with CTRL+Q!!)

CTRL+S = Save file

CTRL+SHIFT+S = Save file As

CTRL+ALT+SHIFT+S = Save for web 

CTRL+Q = Quit photoshop

CTRL+A = Select all

CTRL+D = Deselect

CTRL+E = Merge Down (more about layers later on..)

CTRL+R = Rulers visible (the things you drag guidelines out from..)

CTRL+T = Transform selection (Scale and rotate..)

CTRL+U = Change image Hue, Saturation and Lightness 

CTRL+I = Inverse

CTRL+F = Repeat last used filter

CTRL+K = Preferences

CTRL+L = Levels

CTRL+Z = Undo (something you just can´t live without. Fact.)

CTRL+X = Cut

CTRL+C = Copy

CTRL+V = Paste

CTRL+B = Color balance

CTRL+M = Curves

CTRL+Space = Zoom In

CTRL+ALT+Space = Zoom Out

D = Set Colors to Default

X = Change Foreground color with Background color

CTRL+SHIFT+E = Flatten image

CTRL+SHIFT+T = Transform again

CTRL+SHIFT+U