General

FunctionKeyNotes
Brush Settings (menu)Window > Brush Settings
Tool Preset (menu)Window
Adjust Brush Size and HardnessAlt + Right ClickMove mouse horizontally to change size and vertically to change hardness
Adjust Brush Opacity1 - 01 is 10%, 9 is 90% and 0 is 100%
UndoCtrl + Z
RedoCtrl + Shift + Z

Tools

FunctionKeyNotes
BrushB
EraserE
LassoL
EyedropperAlt
Clone StampS
Spot HealingJ

Interface

FunctionKeyNotes
Hide All PanelsTab
Hide Right PanelShift + Tab

Layers

FunctionKeyNotes
New LayerCtrl + Shift + N
Duplicate LayerCtrl + JWorks with tools
Merge Layer DownCtrl + EWhen multiple layers are selected, all are merged together
Group LayersCtrl + G
Ungroup LayersCtrl + Shift + G
Create Layer Using All Selected LayersCtrl + Shift + Alt + E

Selecting

FunctionKeyNotes
Select All Pixels On LayerCtrl + LMB (on layer thumbnail)
Select AllCtrl + A
Deselect AllCtrl + D
Reload Last SelectionCtrl + Shift + D
Inverse selectionCtrl + Shift + I
Add To SelectionHold Shift
Remove From SelectionHold Alt

Transforming

FunctionKeyNotes
Move ToolVClick and pull around any layer
Image Size (window)Ctrl + Alt + I
Transform ObjectCtrl + TMore advanced version of move tool. Doesn’t work on locked layers
Scale Object from CenterHold Alt (Transform Mode)
Scale with Free Aspect RatioHold Shift (Transform Mode)
Pull Transform PointsHold Ctrl (Transform Mode)

Dialog Boxes

FunctionKeyNotes
Reveal Reset Button in MenusHold Alt
FunctionKeyNotes
Rotate ViewRHolding**R** will revert to the previous tool when let go.
Move ViewHold Space or HHolding H will revert to the previous tool when let go.
Zoom in / outHold Alt + Scroll Wheel or Ctrl + + / -
Switch to Next ImageCtrl + Tab
Switch to Previous ImageCtrl + Shift + Tab
Maximize ViewCtrl + 0

Other

FunctionKeyNotes
Reset ColorsDResets foreground and background colors to default
Cycle Active ColorXFlips foreground and background color
Fill Selection With Foreground ColorAlt + Backspace
Fill Selection With Background ColorCtrl + Backspace
Desaturate ImageCtrl + Shift + U
Export (window)Ctrl + Shift + Alt + W
Save As (window)Ctrl + Shift + S
Straight LineShift
Layer Style (window)

https://helpx.adobe.com/photoshop/using/default-keyboard-shortcuts.html