Useful shortcuts that I tend to forget:
Both edit and object mode:
S = scale (S + (X,Y,Z ) = scale on axis only), (S + SHIFT + (X,Y,Z ) = scale other axis than… locking selected axis)
R = rotate (R+ (X,Y,Z )= rotate on axis only), (R + SHIFT + (X,Y,Z ) = rotate other axis than… locking selected axis)
5 = switch between orthographic / perspective projection
1 = front view (CTRL + 1 = back)
3 = right view (CTRL + 3 = left)
7 = top view (CTRL + 7 = bottom)
In edit mode:
E = extrude
ALT + A = shrink / flatten
K = cut
F = fill (make edge / face)
I = inset (faces only)
SHIFT + D = duplicate
GG = edge slide
CTRL + I = select inverse
CTRL + R = Loop subdivide
W (specials) = Smooth, etc.
CTRL + Tab = switch between select modes (vert, edge, face)
CTRL + E = Edges menu
CTRL + F = Faces menu
Object mode:
SHIFT + A = add (a mesh, curve etc.)
X = delete
General:
CRTL + Z = undo
CTRL + Y = redo
B = rectangular area select
C = circle area select
O = proportional editing
H = hide
ALT + H= unhide
M = move to layer
A = select all / unselect all
Z = switch between shading (wireframe / solid in 3d view)