In this list you can see most important hotkeys for the GIMP under Linux (most of them work on Windows as well). All keys can be individually assigned: File / Preferences / Interface / Hotkeys.
Help
Help	F1
Context Help	Shift+F1
Toolbox
Rect Select	R
Ellipse Select	E
Free Select	F
Fuzzy Select	U
Select By Color	Shift+O
Scissors	I
Paths	B
Color Picker	O
Move	M
Crop and Resize	Shift+C
Rotate	Shift+R
Scale	Shift+T
Shear	Shift+S
Perspective	Shift+P
Flip	Shift+F
Text	T
Bucket Fill	Shift+B
Blend	L
Pencil	N
Paintbrush	P
Eraser	Shift+E
Airbrush	A
Ink	K
Clone	C
Convolve	V
Smudge	S
Dodge/Burn	Shift+D
Swap Colors	X
Default Colors	D
File
New image	Ctrl+N
Open image	Ctrl+O
Open image as new layer	Ctrl+Alt+O
Duplicate image	Ctrl+D
Open recent image 01	Ctrl+1
Open recent image 02	Ctrl+2
Open recent image 03	Ctrl+3
Open recent image 04	Ctrl+4
Open recent image 05	Ctrl+5
Open recent image 06	Ctrl+6
Open recent image 07	Ctrl+7
Open recent image 08	Ctrl+8
Open recent image 09	Ctrl+9
Open recent image 10	Ctrl+0
Save image	Ctrl+S
Save under a new name	Shift+Ctrl+S
Quit	Ctrl+Q
Dialogs
Layers	Ctrl+L
Brushes	Shift+Ctrl+B
Patterns	Shift+Ctrl+P
Gradients	Ctrl+G
Tool-Options	Shift+Ctrl+T
Palettes	Ctrl+P
Info window	Shift+Ctrl+I
Navigation window	Shift+Ctrl+N
Close the window	Alt+F4
Jump to next widget	Tab
Jump to previous widget	Shift+Tab
Set the new value	Enter
Activate current button or list	Space
In a multi-tab dialog, switch tabs	Ctrl+Alt+PgUp
Open Location	Shift+L
Up-Folder	Alt+ up
Down-Folder	Alt+ down
Home-Folder	Alt+Home
Close Dialog	Esc
View
Main Menu	F10
Drop-down Menu	Shift+F10
Toggle fullscreen	F11
Toggle quickmask	Shift+Q
Close document window	Ctrl+W
Zoom in	+ or Ctrl+Mousewheel
Zoom out	- or Ctrl+Mousewheel
Zoom 1:1	1
Shrink wrap	Ctrl+E
Fit image in window	Shift+Ctrl+E
Toggle rulers	Shift+Ctrl+R
Toggle guides	Shift+Ctrl+T
Edit
Undo	Ctrl+Z
Redo	Ctrl+Y
Copy selection	Ctrl+C
Cut selection	Ctrl+X
Copy visible	Ctrl+Shift+C
Paste as new image	Ctrl+Shift+V
Paste clipboard	Ctrl+V
Clears selection	Ctrl+K
Named copy selection	Shift+Ctrl+C
Named cut selection	Shift+Ctrl+X
Named paste clipboard	Shift+Ctrl+V
Fill with FG Color	Ctrl+,
Fill with BG Color	Ctrl+.
Fill with Pattern	Ctrl+:
Layers
Select the layer above	PgUp
Select the layer below	PgDn
Select the first layer	Home
Select the last layer	End
Merge visible layers	Ctrl+M
Anchar layer	Ctrl+H
Selections
Toggle selections	Ctrl+T
Select all	Ctrl+A
Select none	Shift+Ctrl+A
Invert selection	Ctrl+I
Float selection	Shift+Ctrl+L
Path to selection	Shift+V
Plug-ins
Repeat last plug-in	Ctrl+F
Reshow last plug-in
