Update: Most or all of these courses have now been deleted from Codecademy's website, so this is essentially a collection of dead links now. You can see the current Codecademy courses at https://www.codecademy.com/catalog/subject/all.

Here are some of the "hidden" courses on Codecademy that I've found:

(Old) Make a Website: https://www.codecademy.com/skills/make-a-website

Web Projects: https://www.codecademy.com/tracks/projects

Code Year: https://www.codecademy.com/en/tracks/code-year

Hour of Code - Sun, Earth, and Code: https://www.codecademy.com/en/courses/web-beginner-en-ymqg0/0/1

Teach Yourself Python: https://www.codecademy.com/courses/python-beginner-en-fymF4/0/1

Data management for scientists: https://www.codecademy.com/courses/data-management-for-scientists/0/1

Enhance your website: https://www.codecademy.com/courses/web-beginner-en-AgcGq/0/1

Reading or Beginning HTML: https://www.codecademy.com/courses/web-beginner-en-uITVm/0/1

HTML BASICS: https://www.codecademy.com/courses/web-beginner-en-MWF0C-FYSv3-r1rYm/0/1

How To Make JS Your Own: https://www.codecademy.com/courses/javascript-intermediate-en-2nQQb/0/1

Testing Your Code: https://www.codecademy.com/courses/testing-your-code/0/1

Christmas Presents - Review of Objects: https://www.codecademy.com/courses/javascript-beginner-en-JSxzj/0/1

The Date Object: https://www.codecademy.com/courses/the-date-object/0/1

JQuery (Original): https://www.codecademy.com/en/tracks/jquery-original

CSS: Coding With Style: https://www.codecademy.com/courses/css-coding-with-style/0/1

Advanced CSS Positioning: https://www.codecademy.com/courses/advanced-css-positioning/0/1

CfE Computer Science: https://www.codecademy.com/courses/web-beginner-en-8l45k/0/1

JQuery and Ajax: https://www.codecademy.com/courses/javascript-beginner-en-g7vdk/0/1

Track(2):Intro to the DOM: https://www.codecademy.com/courses/intro-to-the-dom/1/1

Teach Yourself JavaScript: https://www.codecademy.com/en/tracks/teachyourself

Recursion in JavaScript: https://www.codecademy.com/courses/javascript-lesson-205/2/1

Multimedia Projects (Demo): https://www.codecademy.com/tracks/multimedia-demo

AngularJs: https://www.codecademy.com/courses/javascript-advanced-en-2hJ3J/0/1

Web (Original): https://www.codecademy.com/en/tracks/web-original

Hour of code: Start Programming!: https://www.codecademy.com/courses/intro-to-JS-hour-of-code/0/1

Mastering Markdown: https://www.codecademy.com/courses/web-intermediate-en-Bw3bg/0/1

Novice Values & Variables: https://www.codecademy.com/courses/novice-variables/0/1

Web Fundamentals Course[Original]: http://www.codecademy.com/en/tracks/web-original

HTML + JavaScript + CSS: https://www.codecademy.com/courses/html-javascript-css/0/1

Mandrill API: https://www.codecademy.com/en/tracks/mandrill

YouTube API: https://www.codecademy.com/en/tracks/youtube

Twitter API: https://www.codecademy.com/en/tracks/twitter

npr API: https://www.codecademy.com/en/tracks/npr

Evernote API: https://www.codecademy.com/en/tracks/evernote

BOX API: https://www.codecademy.com/en/tracks/box_api

SoundCloud API: https://www.codecademy.com/en/tracks/soundcloud

Big O: https://www.codecademy.com/courses/big-o/0/1

PHP Functions: https://www.codecademy.com/courses/web-beginner-en-7I7Xm/0/1

PHP Object oriented (classes): https://www.codecademy.com/courses/web-beginner-en-bH5s3/0/1

PHP Arrays: https://www.codecademy.com/courses/web-beginner-en-8a35h/0/1