Comparing the demographics of different countries is something I do a lot of in Geography class, and there are several tools that help make that easier for students (see The Best Tools For Comparing Demographics Of Different Countries – I think NationMaster is the best one).

Your Life In Another Country is another simple comparison site. It’s not particularly useful for teaching the concept of demographics, but it might be a nice and easy introduction to the idea before you move on to the more complex tools.