The drawback to this approach, of course, is that it affects the width of not just one cell, but of the entire column and row. The Alignment tab of the Format Cells dialog box. Excel displays the Format Cells dialog box.
However, there is a way you can accomplish the desired goal, although it is somewhat more manual in nature.
The answer is that there is no intrinsic Excel command to add more space, as you can do in Word tables or with the CELLPADDING attribute in an HTML table. Serena asked if there is a way to adjust the text margins with a cell so that there is more white space within a cell.