Three-dimensional scatterplots, references to which VividD and Lars Kotthoff are given, are probably the best example of what you are asking, but I am going to assume that perhaps you are asking the wrong question.
Attempting to simulate three spatial dimensions on a flat screen will always be imperfect and difficult to read data.
However, in D3 very easy to display three different data dimensions. Suppose you use horizontal and vertical layouts for your two variable data, and then size, shape, color, or shading for your third variable.
If all three of your variable data are best represented by continuous numbers, then it is best to use a bubble scatter chart, where your three display dimensions are horizontal position, vertical position and bubble size.

Bubble Scatterplot - click for original
You said that your three dimensions are Customer , Product and content . I don’t know how important content (number or category), but I’m pretty sure that Customer and Product are categories.
Here is an example where two categorical dimensions are used. To arrange a table, each cell in the table contains a circle, measured by a third, numeric dimension.
If your third variable is a category, you can use the form to specify which type of “content” (if any) corresponds to each pair of “customer” and “product”:
d3-bubble-matrix

Here is another application where the third dimension is shown in color, not size. Colors represent a continuous variable, but you can easily select a set of highly contrasting colors to represent categories:

Day / Hour Heatmap
Of course, a simple old stacked bar graph is another way to show two categories and a numeric value:

Stacked bar graphs
And you do not need to dwell on three variable data. If two of the variable data are categories or numbers that you do not mind grouping into categories, you can plot the four variables using the “multiple multiples” method, where you will create a table representing categorical variables, and then repeat the graph two other variables inside each table cells
Like here:

Scatterplot Matrix
Or this application (where the week and day of the week are the two dimensions of the data, and the category / amount is the other two):

Pie chart small multiples
I hope this gave you a lot of ideas ...
Answer source: @AmeliaBR

3D Surface Plot in D3.js

3D Vector Field in D3.js
Answer source : @aturc