As promised, Microsoft has delivered a public Release Candidate (RC) version of Exchange Server 2010. It's available in three ways:

Trial Software

The new Exchange Server 2010 Release Candidate is here. Download this 120-day free release candidate version and try the new features in your own environment. When you register for the Exchange Server 2010 RC software you will automatically receive valuable product evaluation resources assembled in one convenient location.

Virtual Hard Drive

The Microsoft VHD Test Drive Program provides customers with an enhanced server-based software evaluation experience that’s faster, better supported, and more flexible. You can now access the entire catalog of pre-configured Microsoft and partner products and solutions in the VHD format and start evaluating and testing today.

Online Trial

Experience the new world of Software plus Services through Microsoft Exchange Online, which enables you to try all the messaging and calendaring functionality you need with none of the administrative burden.

Enjoy.