I have just completed my first block for Moodle and hope it may also be helpful to others.
this block allows users to adjust the font size of a page by using either a button or the + and - keys on the keyboard.
The block only magnifies text of pages it is on and data is stored in a cookie on the users system. This means that a: The users settings are saved so they dont have to reset the size on every page and b: pages you do not wish to have changed can stay that way.
Customizable variables allow you to set minimum and maximum font sizes as well as the increment at wich the zoom steps change the fonts.
Should you wish for areas to not be resized then set these "noResize" areas by using <div class="noresize">ex....</div> or <font class="noresize">ex....</font> or <p class="noresize">ex....</p>
It is my first block and thus is open to suggestions and changes to help it best suit those who wish to use it.
The block is written for 1.5 Instalation files are included in the file