Most important stuff is topmost.
Move selected: G ( X / Y / Z to define axis, XX / YY / ZZ to define local axis, numeric value to define amount )
Rotate selected: R ( X / Y / Z to define axis, XX / YY / ZZ to define local axis, numeric value to define amount )
Scale selected: S ( X / Y / Z to define axis, XX / YY / ZZ to define local axis, numeric value to define amount )
Add new object: Shift + A
Duplicate object: Shift + D
Add / Remove from selection: Shift + RMB
Box select: B ( MMB-drag to deselect )
Circle select: C ( MWheel to change size, MMB to deselect )
Lasso select: Ctrl + LMB ( Shift + Ctrl + LMB to deselect )
'Select all' / 'Deselect all' toggle: A
'Wireframe view' / 'Solid view' toggle: Z
Make parent: Ctrl + P ( first select the children, then the parent )
Join objects: Ctrl + J ( select the object last into which you want to join )
Zoom to selected: Numpad .
Local View toggle (isolate selection): Numpad /
during moving/rotating/scaling - Restrict one axis: Shift + X / Y / Z
during moving/rotating/scaling - Restrict one local axis: Shift + XX / YY / ZZ
during moving/rotating/scaling - Incremetal behavior: Hold Ctrl
during moving/rotating/scaling - Precision behavior: Hold Shift
Rotate object as trackball: RR
Back View: Ctrl + Numpad 1
Left View: Ctrl + Numpad 3
Bottom View: Ctrl + Numpad 7
Perspective / Orthographic toggle: Numpad 5
View everything ( and center 3D-cursor to origin ): Shift + C
Full screen ( the window under mouse cursor ): Shift + Space
Tools sidebar ( in the window under mouse cursor ): T
Properties sidebar ( in the window under mouse cursor ): N
Show / Hide Render View toggle: F11
Next Render Slot ( in render view ): J
Previous Render Slot ( in render view): Alt + J
Save Blender File as... : Ctrl + Shift + S or F2
Open Blender File: Ctrl + O or F1