Thought of this yesterday afternoon and wanted to get it "on the record" before the keynote. I have no insider information and have not seen this specific prediction elsewhere; it's just a personal guess based on the "There's Something In The Air" slogan and connecting a few existing dots.
-A MacBook (and/or the rumored subnotebook) with a built-in HSDPA modem for high speed data access on the AT&T network. It would leverage Apple's existing carrier relationships, give them a new slice of coveted subscription revenue, and simplify the usually clunky process of activating and configuring an aircard.
We'll see what develops soon enough. Feel free to mock or praise me in the comments.