Update: Microsoft announced two tablets based on the Surface interface, called the Surface RT and Surface Pro, and accompanying touch-based and tactile keyboards. See the liveblog linked above for the full details, and our post-announcement coverage.

Microsoft will make a "major announcement" at a media event at Milk Studios in Los Angeles, starting at 3:30 PDT today. The announcement is widely believed to be a new Microsoft tablet device, but just what sort of tablet has been the source of wide-ranging rumor and speculation.

Several sites have reported that the device would be a cross between Barnes & Noble's Nook e-reader and a device for streaming video content from the XBox, in an effort to compete with Amazon's Android-based Kindle Fire. This morning, a Barnes & Noble spokesman denied that it was involved with the announcement.

Other rumors include a tablet that ties into the XBox platform based on Microsoft's Surface touch-based interface. The gaming news site Shifted2U posted alleged leaked documents over the weekend for the specifications of "XBox Surface," a gaming and entertainment tablet that acts as an extension to the XBox. The 7-inch tablet itself, built on a custom IBM processor, is an extension of a new XBox "stationary computing device.

Whatever Microsoft has in store, Ars Technica's Peter Bright will be covering the event live from Los Angeles as it happens.

Listing image by Robert Scoble