Ok if you hate gimmicks don't even read this.
Invisible Zone £10.99
http://www.magicbox.uk.com/product.php/000/00238/
You have a little plastic box with the words Invisible Zone across the front, after a bit of patter about making things invisible you tell the spec, which could be a child as easily as an adult, that you will show them what you mean.
You take a bic type pen which can be momenterily handled by the spec but not examined and push it into the side of the box, it enters and exits but can not be seen in the middle ( despite there being no front or back to the box ). You can push the pen in and out and both ends can clearly be seen but the middle is completely invisible. Quite a stunning visual effect.
Re-sets instantly and is very easy to do, maybe 5 minutes practise. Only negative is there is a small angle issue in that you wouldn't want anyone behind you.
Great little trick and something a bit different.