An Experimental Life

(From Jungmin Escobar with added material from Rob)
So, here's a list of super useful shortcuts in Photoshop that I've found. They should work in almost all versions.

B - Brush Tool
E - Eraser Tool
[ - Decrease Brush Size
] - Increase Brush Size
Z - Zoom Tool (Alt+Z to zoom out)
Alt+plus sign - Zoom entire image
Alt+minus sign -Zoom out entire image
I - Eyedropper tool
V - Move Tool
G - Paint Bucket
W - Magic Wand
Alt+D - deselect selected area
Alt+H - Hide selection boundaries
C - Crop
M - Marque Selector
T - Text Tool
L - Lasso Tool
X - Swap Foreground and Background Colors
Shift+F5 - Fill Selection
Ctrl+A - Select Canvas
Ctrl+T - Free Transform
F - Fullscreen
Tab - Hides Toolbars
Spacebar (Hold Down) - Drag Canvas
Hold Alt while using the brush or paint bucket tools to get the color picker

On every tool, you should be able to hold Shift and push the appropriate key to change the tool. Pushing Shift+G will change between the Paint Bucket and Gradient Tools.

I know there's a lot more, but these are the ones I use the most.