Como una alternativa simple y rápida de usar al Generador de contraseñas aleatorias para Excel, hice esta adaptación Javascript del código de la función de generación aleatoria de contraseñas… Podés ver el código fuente más abajo…

Caracteres


Mayúsculas Minúsculas Números

Contraseña Aleatoria

El código está liberado bajo la licencia GNU GPL v3…
En caso de que quieras ver el código de la función sin tener que buscar en el código fuente de la página:

/*************************************************************************************************
Random Password Generator by NeoEGM

Copyright (C) 2009 Ezequiel Gastón Miravalles

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*************************************************************************************************/

/*************************************************************************************************
Software: Random Password Generator by NeoEGM
Author: Ezequiel Gastón Miravalles
Website: http://www.neoegm.com/software/random-password-generator/
License: GNU GPL v3 (read above)
*************************************************************************************************/

function RandomPassword(Length, Upper, Numbers, Lower)
{
	Upper = typeof(Upper) != 'undefined' ? Upper : true;
	Numbers = typeof(Numbers) != 'undefined' ? Numbers : true;
	Lower = typeof(Lower) != 'undefined' ? Lower : true;
	
    if (!Upper && !Lower && !Numbers)
		return "";

    var Ret = "";
    var Num;
    var Repeat;

    Chars = 26 * 2 + 10;	//26 (a-z) + 26 (A-Z) + 10 (0-9)
	//a-z = 97-122
	//A-Z = 65-90
	//0-9 = 48-57

    for (i = 1; i <= Length; i++)
	{
        Repeat = false;

        Num = Math.floor(Math.random()*Chars);

        if (Num < 26)
            if (Lower)
                Ret = Ret + String.fromCharCode(Num + 97);
            else
                Repeat = true;
        else if (Num < 52)
            if (Upper)
                Ret = Ret + String.fromCharCode(Num - 26 + 65);
            else
                Repeat = true;
        else if (Num < 62)
            if (Numbers)
                Ret = Ret + String.fromCharCode(Num - 52 + 48);
            else
                Repeat = true;

        if (Repeat)
            i--;
	}

    return Ret;
}