Symmetry groups of possible dice faces (cubical d6 dice)

# Face Group
0 Face 0 D4
1 Face 1 D4
2 Face 2 D2d
3 Face 3 D2d
4 Face 4 D4
5 Face 5 D4
6 Face 6 D2x
7 Face 7 D2x
8 Face 8 D4
9 Face 9 D4
The die faces' symmetry groups are the symmetry group of the square and two of its subgroups. They are all rotation-reflection (dihedral) groups.
Group Elements
D2x Rotations: 0°, 180°
Reflections: axial: horizontal and vertical
D2d Rotations: 0°, 180°
Reflections: diagonal: both diagonals
D4 Rotations: 0°, 90°, 180°, 270°
Reflections: both axes and both diagonals

The die itself, ignoring face markers, has octahedral symmetry, Oh.
Faces on a Die: Their Placement

All Faces
Opposite faces usually add up to 7, but within this constraint, there are 24 = 16 possible arrangements:
Non-Cubical Dice

The most common kind is the coin. Flipping a coin is eseentially using it as a d2 die.

Players of tabletop role-playing games have used numerous kinds of dice, distinguished by them as d<number>. They include:
Family Number of Sides
Platonic solids 4, 6, 8, 12, 20
Catalan solids 12, 24, 30, 48, 60, 120
Bipyramids Even numbers ≥ 6
Trapezohedra Even numbers ≥ 6
Prisms Integers ≥ 3
Antiprisms Even numbers ≥ 2

Degeneracies:

To my symmetry index page