The basic iCloud account is free, and includes 5GB of storage for Backup (of your iPhone, not your Mac), Mail, Photo Journal and iWork Documents (not general file storage). A new iCloud account gets an @icloud.com address - new @me.com addresses cannot be created, though existing ones will be maintained. You don't have to pay anything unless you want additional storage. MobileMe migratees get an additional complimentary storage until September 30th 2013.
This page contains detailed information on iCloud: