I appologise if you already know all of these, but this is something I post in every forum because I find it very helpful, and I know others will.
These are really helpful to me, and aid me to make pictures quicker, rather than having to click everywhere all the time. As I remember more, I will add them, and if you know of any you think should be on here, please post them.
Ctrl+N-New Document
M-Marquee Tool
B-Brush Tool
V-Move Tool
G-Fill Tool
Z-Magnify Tool
P-Pen Tool
L-Lasso Tool
W-Magic Wand Tool
E-Eraser Tool
C-Crop Tool
K-Slice Tool
T-Text Tool
U-Custom Shape Tool/Line Tool etc
Ctrl+Shft+N-New Layer
Alt+Backspace-Fill with Foreground Colour
Ctrl+Backspace-Fill with Backgroun Colour
Ctrl+A-Select all
Shift+Arrow-Moves selected object 10 pixels
D-Restores colour defaults
X-Switches between Background and Foreground colour
Ctrl+T-Transform
Ctrl+Alt+Z-Undo last
Ctrl+Shift+Z-Redo Last
Hold Shift-Makes a perfect circle or square using the marquee tool.
Shift+Letter-Ok, if I've got Rectangular Marquee tool selected, to chage to Elliptical Marquee Tool, just press Shift, and in this case M, it will cycle through each one.
Ctrl+Shift+I-Inverses the selection
Crtl+R- Brings up Rulers.
Direction Arrow-1 pixel nudge.
Ctrl+Shift+I-Inverses selection