Windows Phone 8 devices that we had heard about. That would give Microsoft pretty solid coverage, with the Nokia announcement of WP8 devices expected tomorrow, then HTC on the 19th, the Windows 8 release in October, and Windows Phone 8 in November. It will be hard to avoid Microsoft news over the next couple months.
It is also possible that this will be the official reboot of HTC's tablet attempts with the announcement of that iMac-looking tablet that we saw last week. We haven't really heard about any flagship Android events on the horizon though, so that seems less likely, especially given that the timing links with the Windows Phone 8 rumors we had heard before.
The event will be in NYC on September 19th at 11AM EST, and we'll be there to let you know what's coming!