Question: I am a product/project manager for a product we've created. We have customers using the product, which we are continually updating as it is Web based.

What are some tools and techniques for managing communications with clients regarding product updates?

Answer: 
I like the way LiquidPlanner does it. They use the space on the right side column of the dashboard once a user logs in.

![LiquidPlanner dashboard](https://i.stack.imgur.com/ZogWc.gif)

This way whenever I log in I'll see their update and can click to find out more. If you're already using a web based system than why not take advantage of letting announcements and other news reside where users can easily find them.
If your updates are small and can be made public, I would include Twitter in your list. Take [the Twitter stream for OmniFocus](http://twitter.com/#!/OmniFocus), [or for FreshBooks](http://twitter.com/#!/FreshBooks) as examples.