Visit Apple’s main website today, and the first thing you see is a big message: “Tomorrow is just another day. That you’ll never forget. Check back here tomorrow for an exciting announcement from iTunes.”So what does Apple have planned? Plenty of blogs are jumping to the ‘subscription/cloud-based iTunes’ conclusion, although that would surely require licensing to be in place already. Unless Apple plans to announce the service as more leverage to get labels to sign up, of course…Tuesday, of course, is the day that new albums are released in the US, so it could be a content announcement. And you don’t need us to tell you what kind of release would deserve this kind of build-up – Beatles? We’ll have to dust down our venerable Yellow Submarine iPod rumour again.iTunes isn’t just about music of course: this could be a film and/or TV-related announcement, tied into the Apple TV set-top box. And if you want a really long shot, how about the iTunes Store opening up to non-Apple devices? We did say it was a really long shot.All will be revealed at 3pm GMT tomorrow, and we’ll be reporting it on the Music Ally blog as it becomes clear. Oh, and Google tells us that John Lennon’s ‘How Do You Sleep’ song – targeted at a post-Beatles Paul McCartney – included the line “Since you’ve gone, you’re just another day.” Just saying… (yes, we know Tomorrow’s Just Another Day is a Madness song, but that’s no good for rumour-mongering).