Starting with a tweet yesterday from John Golden (@mathhombre)
— John Golden (@mathhombre) August 13, 2012
I followed a trail which (thanks to a comment from Pete Bocken on the post that John Golden linked to) led me to the WordPress plugin EmbedIt Pro by SuperThemes, which has allowed me to do something which seems like it ought to be simple, but has frustrated and stymied me up until now: embed a GeoGebra applet in a WordPress post! With EmbedItPro, it really couldn't be simpler. Install and activate the plugin, click on HTML Snippets, paste in your HTML code, publish that, and get a snippet to embed in the visual post editor. Voilà!
Thank you SuperThemes!