Crocodile Clips-
http://www.crocodile-clips.com is available in a Mac OS X version - different packages available for maths, physics, chemistry, design technology etc. Well worth a look.
Most of the other useful software that I use is pc only (things like 2D-Design for CAD and CAM work, PCB Design and Make, and more specialist stuff for working with PICs). Xara X is pc only at the moment, but a Mac version is hopefully coming out soon - the best program I've ever used for teaching vector graphics, and very useful for Media Studies, Art Graphics, Design Technology.
Microsoft Excel, often overlooked, has to have a vote for being one of the most versatile applications - a wide range of uses in Maths and ICT (of course), Design Technology and Science (very useful for modelling equations, esp in conjunction with graphs/charts because of its ability to 'live update' a graph as the data is changed.
Personally, I'm a strong believer in using industry standard packages wherever possible and appropriate. I use Photoshop, InDesign and MS Office a lot. I steer clear of AutoCAD (too expensive and too complicated), and only use Illustrator for older students (16+) because its more difficult than Xara and kids get frustrated with it, esp the pen tool.
The worst use of IT in the classroom is the internet. What a time waster. Most teachers don't know how to use it anyway. Get a free app to download the web sites you want students to work with - it'll avoid all the problems with kids being on games sites, MSN etc when they're meant to be working.
