mkpass is a simple command line utility to generate secure random passwords. You can easily redirect these to a clipboard or copy and paste as needed.
I use a password manager and generate random passwords every time I need one. And while most password managers include a generator, there are times I need one outside of that.
The code is written in java so it should run on any OS that supports it. Lastly, the idea and core code came from a Wikipedia article. I just took this and...
An easy-to-use generator for large numbers of passwords.
Originally for my school's IT Department, I have now released the source code under the GNU GPL. It supports the random generation of huge numbers of passwords that can be determined in a variety of ways.