I signed up Google Apps for my domain today and played around with it, and it’s great! look at what Google says:
Google Apps for Your Domain lets you offer private-labeled email, instant messaging and calendar accounts to all of your users, so they can share ideas and work more effectively. These services are all unified by the start page, a unique, dynamic page where your users can preview their inboxes and calendars, browse content and links that you choose, search the web, and further customize the page to their liking. You can also design and publish web pages for your domain. (Google Inc.)
And this is total free, I also can add many email accounts for my domain which are powered by Gmail. As long as you are not seriously considering privacy and security, this is one of the best email services for your domain.
Here are some screen shots:
RIght now, it’s still in Beta, it doesn’t provide many function for an enterprise; but it’s good enough for small business and individuals.