Google Apps for Your Domain is a free service (atleast during the beta period) that lets companies (and anyone with a domain) offer different applications to their users.
Google Apps started with offering just Gmail and then moved on to offer Google Calendar, Google Talk and Google PageCreator.
Added to this list is the Custom Start Page:
The start page lets you easily create a unique, dynamic place for internal or external users to find relevant, essential information, preview their inboxes and calendars, and search the web. You customize the layout, header information and color scheme, as well as the page’s default content, which can include Google Personalized Homepage modules, your organization’s custom content and links, and RSS feeds. After users log in, they can further customize the start page so it’s just right.
I also plan on implementing the same for few of my clients. Since a good deal is easily customizable, you have shared address book if you please a great number of email addresses (you can choose while signing up), it becomes a very feasible solution for a small company.
Once the beta period is over these services will be paid. However, those who signup during this period shall receive the service free forever!
If you wish to give this try you can signup here.
Remember, you need to have your own domain. You will also need to have the ability to modify the MX entries for your domain or your email will never work.