Very nice beginning… but if you can squeeze in one more project, you will have a winner. Specifically an intro robotics project if that is possible. Granted the working parts would be a bit more expensive (if Arduino can even do robotics).
Another vote here for Brad’s suggestion - an introductory robotics project would be very nice.
Of course, I have thought about writing a robotics chapter and with the Arduino it is possible to build more or less sophisticated robots. There are two problems, though: it is quite expensive and it really isn’t for beginners. Still I think with the motors and the sensor chapters we build a good foundation for some robotics experiments.
And now that I know there is some interest in robotics… :-)
Yeah… After I posted this request… It dawned on me that the robot project could get $$$ pretty quickly and figured thats probably why you didn’t include a chapter for it in the first place.