Last winter I published a chart that compared the key features of five popular student response platforms. In the nine months since then more student response tools have come onto the market. This morning I added those tools my chart. The chart is embedded below as PDF hosted by Box.com. You can also get a Google Documents copy of it by clicking here.
Update: Since the time that I published this chart, there have been some variations created by well-meaning teachers. There are more tools than can fit into a concise chart. I chose the ones that I like the best and will endorse publicly.