Databases and SQL, everyone developer needs to know about them. They are easy to learn, incredibly ubiquitous and actually quite fun to work with. Have them sta

Databases and SQL, everyone developer needs to know about them. They are easy to learn, incredibly ubiquitous and actually quite fun to work with. Have them start out simple by downloading MySQL and reading, say, <a href="http://www.w3schools.com/>W3 http://www.w3schools.com/>W3 Schools tutorials</a>. Regular expressions. Very useful no matter which area (desktop, web, mobile) you specialize in. HCI, usability, interaction design. They should atleast know enough about usability and design to appreciate its importance and avoid The Usual Mistakes (TM). Using and administering web server software. Learn about Apache and the most common modules (e.g. mod_rewrite) because the odds are pretty high that you'll have to set up a web server in the future.