I'm an Engineering lecturer at Derby College in the UK where I teach Mathematics, Science, Materials and Manufacturing Systems subjects mostly to BTEC National Certificate level. However I also teach HND and Foundation degree students.
 

1. GeoGebra - A Dynamic Mathematics program, I am using it to plot functions, and create animated science work sheets and interactive content for Maths and Science. It is excellent and licensed under the GPL, there is a reasonable amount of documentation for it and examples abound on the internet. Just Google Geogebra. It creates Java applets that interact with your students.

2. Notepad - editing HTML and Javascript

3. PortableApps.com - A number of portable applications including open office that will run on a memory stick without affecting the computer you are using. Again under a GPL license.

4. Google - Search engine

5. Adobe Reader - PDF reader

6. Powerpoint - Presentation program

7. Teachers report assistant

8. Word

9. Excel

10. Audacity - Record, edit and manage sound files.