Drawing a cube seems to be a fairly common task! There are a few other questions here that involve drawing cubes. It's not always right to merge them, but I thought it worth doing a little more than just linking. So this answer is a Community Wiki (so almost anyone can update it) list of the other cubical questions here. The intent is to include at least one representative picture from the answers.
Need help creating a 3D cube from a 2D set of nodes in TikZNeed help creating a 3D cube from a 2D set of nodes in TikZ
Tom Bombadil'sTom Bombadil's answer here is well on the way to being a package, showing that he has mastery over cubes as well as rings.
How to draw a cube with TikZ where all faces have a distinct color?How to draw a cube with TikZ where all faces have a distinct color?
The accepted answer yields the first image, and the second is a another from the same question:
Is there a way to draw TikZ lines on the "inside" or "outside" of a path?Is there a way to draw TikZ lines on the "inside" or "outside" of a path?
Although not obviously about cubes, the motivation was to draw a cube and get the corners right.
How to draw parallelepiped and cube with LaTeX?How to draw parallelepiped and cube with LaTeX?
One answeranswer provides a pic
for drawing annotated cuboids like these: