I don't think that the x-bar (or any other letter-bar) is included in a standard font set. Normally, the typesetting program will add the bar itself by writing the letter and then drawing the line over the top. If you want a symbol like this in Word, you should be able to use the Microsoft Equation plugin (something like Insert > Object > Microsoft Equation x.x). You can use the dialog that appears to create the x-bar (and a whole equation that includes it). If you're looking to use mathematics symbols seriously, consider the LaTeX typesetting system.

x̄
For the web at least, here is how you can do it.
http://www.personal.psu.edu/ejp10/psu/gotunicode/statsym.html

This should apply to regular programs as well, I'm not entirely clear on unicode support in non-web contexts, but it appears to work in most. For example copy and paste the x here. It should work in most apps.

BTW. Character map doesn't show it because this is actually one regular character and then a special modifier TO the character. The x here may not be correct, but the modifier should be.

For typesetting formulas in academia the usual tool is TeX. TeX editors are available as free software for most operating systems. The TeX system will create any symbol used in mathematics and statistics.

Great! Thanks everyone for your help.

As an alternative to Word's equation editor, this page explains how to construct an overstrike character and assign a shortcut key.

But for doing statistics or other math, wouldn't a math pi font be a better solution in the long run? The American Mathematical Society has free Postscript distributions of Computer Modern and AMSFonts at http://www.ams.org/tex/type1-fonts.html. TrueType versions are on the Mozilla website at http://www.mozilla.org/projects/mathml/fonts/.
Wolfram's downloadable Mathematica 6.0 fonts are at http://support.wolfram.com/mathematica/systems/windows/general/latestfonts.html, and MathType fonts are at http://www.dessci.com/en/dl/fonts/.

(These are all properly licensed or donated fonts, so I don't believe the links violate any Typophile rules.)

Gus

But is there an x bar character in those AMS fonts? I haven't set maths for a long time, but I recall that the x bar was created by an overline on the x, not a specific character.

> But is there an x bar character in those AMS fonts?

You're probably right. I, too, don't work with scientific material any more and don't have any math fonts installed, but I did have a vague memory of using a font that had an x-bar, and those fonts are the usual suspects. Of course, given that this is Monday, I might be thinking of h-bar.