Recently at work I developed a quick and dirty Google Calendar plugin for WordPress called gCal. In all simplicity, it needed to grab the public calendar XML file, parse it, shoot out a list and provide event details in a JavaScript modal popup. It is very basic, with only one view option and few backend settings, but it got the job done. In the last week I worked on the plugin, filling it out some. There is now an administrative panel via your WordPress dashboard. Currently the only setting is the Google account you wish to access the Google calendar of, which cut the shortcode down from "gcal gmail=" to "gcal".
The next release will focus on different views. Right now the plugin merely does a list of the 25 events returned, and provides a link that pops up the modal. At the moment a full calendar display, like the default Google calendar view, is in the works.
I plan on posting updates as development continues.