50 useful keyboard shortcuts

V – Move tool
M – Rectangular Marquee tool,Elliptical Marquee tool
L – Lasso tool,Polygonal Lasso tool, Magnetic Lasso tool
W – Magic Wand tool,Quick Selection tool
C – Crop tool, Slice tool, Slice Select tool
I – Eyedropper tool, Color Sampler tool, Ruler tool, Note tool, Count tool
J – Spot Healing Brush tool, Healing Brush tool, Patch tool, Red Eye tool
B – Brush tool, Pencil tool, Color Replacement tool
S – Clone Stamp tool,Pattern Stamp tool
Y – History Brush tool,Art History Brush tool
E -Eraser tool, Background Eraser tool,Magic Eraser tool
G – Gradient tool,Paint Bucket tool
O – Dodge tool, Burn tool, Sponge tool
P – Pen tool, Freeform Pen tool
T – Horizontal Type tool, Vertical Type tool, Horizontal Type mask tool,Vertical Type mask tool
A – Path Selection tool, Direct Selection tool
U – Rectangle tool,Rounded Rectangle tool,Ellipse tool,Polygon tool,Line tool,Custom Shape tool
K - 3D Rotate tool,3D Roll tool,3D Pan tool,3D Slide tool,3D Scale tool
N – 3D Orbit tool ,3D Roll View tool,3D Pan View tool, 3D Walk View tool, 3D Zoom tool
H – Hand tool
R – Rotate View tool
Z – Zoom tool

Brushes panel keys are important too some of the tools are brushes based.
Delete brush – Alt-click brush
Rename brush – Double-click brush
Change brush size – Alt + right click + drag
Decrease/increase brush softness/hardness - Alt + Shift + right click + drag
Select previous/next brush size – , (comma) or . (period)
Select first/last brush – Shift + , (comma) or . (period)
Display precise cross hair for brushes – Caps Lock or Shift + Caps Lock
Toggle airbrush option - Shift + Alt + P

Transforming selections, select borders and paths are also important and here are your keyboard shortcuts:
Transform from center or reflect - Alt
Constrain – Shift
Distort – Control
Apply – Enter
Cancel – Control + . (period) or Esc
Free transform with duplicate data - Control + Alt + T
Transform again with duplicate data – Control + Shift + Alt + T

The Layer panel also has shortcuts that you may use, here are some:
Group layers – Control + G
Ungroup layers – Control + Shift + G
Create/release clipping mask – Control + Alt + G
Select all layers - Control + Alt + A
Merge visible layers – Control + Shift + E
Edit layer style – Double-click layer
Show/hide this layer/layer group only or all layers/layer groups – Right-click the eye icon
Disable/enable vector mask – Shift-click vector mask thumbnail
Toggle lock transparency for target layer, or last applied lock – / (forward slash)
Edit layer effect/style, options – Double-click layer effect/style
Move layer to bottom or top – Control + Shift + [ or ]
Copy current layer to layer below – Alt + Merge Down command from the Panel pop‑up menu
Merge all visible layers to a new layer above the currently selected layer – Alt + Merge Visible command from the Panel pop‑up menu