You can now become part of a beta test to get Gmail for your domain; more from the site:

"This special beta test lets you give Gmail, Google's webmail service, to every user at your domain. Gmail for your domain is hosted by Google, so there's no hardware or software for you to install or maintain.

• Gmail - 2 gigabytes of storage and search tools that help users find information fast.
• Control Panel - Easily manage user accounts, aliases and mailing lists."

Not sure how long the beta test is going to be going for, so if you're interested, make sure you sign up.

Related: Google opened Gmail to the public back in August; now anyone can get a Gmail account (no invitation needed) as long as they sign up with their mobile phone; if you for some reason can't do that, you'll still need an invite.