Wavr is an easy way to embed google wave into wordpress featuring shortcode and a tinymce button.
On the Sandbox: Simply use the Debug-menu on the top-right. Open the wave on Google Wave and click on Debug -> Get Current Wave ID. Make sure you use the full wave id (something like wavesandbox.com!w+MNJWKLNa%A) (Thanks to Michael Kamleitner )
On the wave preview (Or when you don't have the Debug menu): Open the wave and look at the location bar. You will see something like this: https://wave.google.com/wave/?pli=1#restored:wave:googlewave.com!w%252Big2e7T0UC.13
The wave id is the part after
wave:, in this case,
You will have to take the part after the '.' out, and replace %252B with + so
in our case the final wave id would be:
Update: The plugin will try to guess the wave id if you paste the full url into the wave id field.