Click to download RandomPassword a freeware random password generator. Unzip the file and click Setup.exe to install the program on a Windows® machine.  The C source code is included in the download.

The program uses Marsaglia’s (MWC) multiply with carry generator, which generates sequences of random numbers of about 10^19. See Marsaglia’s post and http://www.stat.fsu.edu/pub/diehard/ for details. The seeds are set initially as the least significant digits of multiples of the system time. The sequence so set is unique with probability zero.The dialog appears as follows:

The password is both shown and copied to the clipboard.

The password will contain both upper and lower case letters and numerals. It is of course possible to add other symbols, but enough is enough. To keep track of the passwords, it is useful to put them in a software package meant to keep then secure -- I use Password Corral myself: http://www.cygnusproductions.com/; which in version 4, has a random password generator. At the present time it’s mixed letters and numerals passwords are not guaranteed to contain numerals. (Some sites check passwords and reject them if both letters and numerals are not present.)