We just bought this one for school this year and it's actually quite good. I was pleasantly surprised actually because it's fairly inexpensive. The only thing I don't like is that it has a pointer that you can't remove.
http://www.rainbowresource.com/product/Microscope+40%2C100%2C400X+%28Model+3000FF%29/010034/1269823041-904626
They do have other models that are more expensive, but both my almost 6 and almost 11 year old kiddos really like this one. It's nice and heavy, easy to use, and the lighting source is great. It also has a diaphragm to allow more/less light aside from the lamp source. The magnification is 10x, 40x, and 400x, and uses an LED light source with a plug in chord.
