Google offers products calls ‘Google Apps for Business’. This includes GMail (email), Google Talk (chat), shared Google Calendars, Google Docs, etc. You can get some information here.

They offer a few different versions with different limitations.

For just $20/year, you get:
-Setup & Configuration
-Update DNS Settings
-Create User Accounts
-Troubleshooting
-Full Support

To compare the editions of Google Apps, click here.

Since Google has done away with their free version, I now support Windows Live for Domains, which you can access here. You can even allow users to register for their own email addresses with your domain.