The rumor mill holds that Microsoft might announce its own tablet on Monday, running Windows 8 RT, the ARM-based tablet version of Windows 8.
The potential Microsoft tablet would probably have a lot of Nook-heavy content, given Microsoft’s relationship with (and investment in) Barnes & Noble. Xbox video streaming might be another prominent feature.
However, I think it’s more likely that the big announcement will revolve around the next-generation Xbox console. Microsoft hasn’t done terribly well with its own branded hardware devices (like the Zune), and making a “Zune tablet” might well flop. But the Xbox has done well, and it makes more sense for Microsoft to double-down on it.