I have experimented with Plugoo chat (http://www.plugoo.com/) on my blog as a quick and easy way for students and parents to contact me. It's simple and syncs up to my Google Talk account which I use from my BlackBerry.
I saw this today on Read Write Web and it's a little different. This lets you have a multi user Facebook style chat on your blog or site. This could add an extra dimension of real time collaboration to what students are working on. It could be a viable back channel during discussions and keep everything in a one stop location.
The free plan supports up to 5 simultaneous users. Prices and numbers of simultaneous users go up from there. It might be worth looking in to if you need something like this.
Does anyone know of something better or alternatives?