Q: I'm always surprised by how little attention we pay to developing the voice as a tool. It's of central importance, but it's taken for granted that we can use it effectively and in ways that are not going to lead to lasting physical damage. All teachers really should be entitled to voice training at all stages of their career. However, September 2005 to July 2006 has been declared "Year of the Teacher's Voice", so we may see improvements.
The resources you need are already in your school. You'll find the experts in the music and drama departments, and they will probably be happy to work with you. And, I don't doubt, with several other teachers who share your need, such as as Inset providers. They will talk about upright posture, pushing your voice out from the diaphragm rather than from the lungs, and about effective breathing. They should also give you practical exercises, such as humming, lowering pitch and so on.
If you need to add weight to your request, visit the Voice Care Network at www.voicecare.org.uk. They will run training sessions for you. That's something that could be organised by your education authority's NQT trainers.
The second part of your question was about alternatives to using your voice to gain the attention of a class. You could use countdown, where you count from five down to one, and then expect quiet, but it will work better if it's a feature of everyone's classroom.
Use silence - say what you want and wait, silently, until you have it. Try holding your hand up, and say "Ready to learn?" Pupils put up their hands to indicate that they're ready.
It doesn't matter what you do, so long as it includes a distinctive gesture, and your pupils are drilled to respond to it quietly. Don't be tempted to use a whistle - the shock effect will wear off, and they are too noisy.