Although not a plugin, an easy solution I have used in the past is to create a new static page and in the HTML editor, followed the instructions for http://www.google.com/support/calendar/bin/answer.py?answer=41207
You could also follow those instructions for inserting into a theme directly (say, in a side-bar).
Edit: This was for showing off to my client what times I’m already booked (Following the embed tutorial on that link, clients could see what times were already booked but not the actual details). Clients would then use a contact form below requesting the date and time. I believe I used http://wordpress.org/extend/plugins/contact-form-7/ for the form with custom options.