Found a couple of neat percent sketches on GeoGebra...
Nice visualization from jholcomb.
(By the way, GeoGebra has gotten input boxes to work in the HTML5/mobile device. Good going!)
Slick discount problem visualization from Anthony Or (orchiming).
Nice double numberline visualization from David Cox.
I debated having the students find the percentages to subtract, but decided to make it optional. There's a short video of how the game works below.
Here it is on GeoGebraTube, for download or for mobile applet.
The test game came out extremely close - most games will be shorter than that. It can be surprisingly suspenseful, though. All students found it pretty playable, and some got very into it. I think the best benefit might be from playing and then using as a context for problems.
Searching through GeoGebraTube, students found two sketches particularly of interest.
Arrange Fractions, Decimals and Percents by dhabecker (who has quite a few rational number sketches), which lets students arrange form numbers of different form from least to greatest. A few students got quite engrossed in this sketch, and the feel of the sketch is terrific - very much like pieces snapping in place.
Estimating Percents by David Cox, which lets students make a first estimate and then a second estimate with the tens showing. Students were happy to see their % error improve from 1st to second guess, and got better quickly through playing. They also made an impromptu game out of it, and I think that would be fun.
Do you know a GeoGebra Percents sketch that you think supports students' understanding?
Here's the results collected so far. Thanks!
PS> there's a follow up post to this one with two more GeoGebra percent activities.