Whether you obtained a copy of iOS 5 as a developer or through less-official channels, you can get a free me.com email address right now. Here's how.
In iOS 5, open the Settings app and tap iCloud. You'll be asked to sign in with your Apple ID. If you already have one, go ahead and sign in and then enable the Mail option. This will give you the opportunity to add a new me.com email address. All you have to do is pick what you want and it will be added. Your login credentials will be your Apple ID but you'll send mail from the account you choose.
If you need or want to create a brand new Apple ID, doing so will let you register a new free MobileMe email account as well. Just continue through the signup steps and eventually you'll be asked to choose an email account and password.
That's all you have to do. This is, of course, a bit of extra work to go through to get a free email address — something you can get more easily through Gmail, Yahoo and other providers — but if you really like the me.com domain it's an option. You won't be able to access webmail but you will be able to use the address on your iOS device and with an IMAP email client by using p02-imap.mail.me.com for the IMAP server (instead of mail.me.com).