Nintendo has released a few specs for the Wii U on its website. The controller has a 6.2 inch, 16:9 touch screen with built-in accelerometer and gyroscope, rumble feature, camera, a microphone, stereo speakers, sensor strip and stylus.

The console itself takes "12-centimeter proprietary high-density optical discs" and existing 12 centimeter Wii discs. It supports screen resolutions up to 1080p and features HDMI, component, S-video, and composite outputs. While the deck features its own flash memory, this can be expanded with an SD card or external USB hard drive.

The system runs on an IBM Power multicore processor.

The console resembles a Wii with rounded corners. Nintendo isn't giving out much in the way of technical detail yet, though we know that the new controllers are wireless, even when displaying high definition video

Update : Here are the specs from the nintendo website :

• Launches: 2012
• Size: Approximately 1.8 inches tall, 6.8 inches wide and 10.5 inches long.
• New Controller: The new controller incorporates a 6.2-inch, 16:9 touch screen and traditional button controls, including two analog Circle Pads. This combination removes the traditional barriers between games, players and the TV by creating a second window into the video game world. The rechargeable controller includes a Power button, Home button, +Control Pad, A/B/X/Y buttons, L/R buttons and ZL/ZR buttons. It includes a built-in accelerometer and gyroscope, rumble feature, camera, a microphone, stereo speakers, a sensor strip and a stylus.
• Other Controls: Up to four Wii Remote™ (or Wii Remote Plus) controllers can be connected at once. The new console supports all Wii™ controllers and input devices, including the Nunchuk™ controller, Classic ControllerTM, Classic Controller ProTM and Wii Balance Board™.
• Media: A single self-loading media bay will play 12-centimeter proprietary high-density optical discs for the new console, as well as 12-centimeter Wii optical discs.
• Video Output: Supports 1080p, 1080i, 720p, 480p and 480i. Compatible cables include HDMI, component, S-video and composite.
• Audio Output: Uses AV Multi Out connector. Six-channel PCM linear output through HDMI.
• Storage: The console will have internal flash memory, as well as the option to expand its memory using either an SD memory card or an external USB hard disk drive.
• CPU: IBM Power®-based multi-core microprocessor.
• Other: Four USB 2.0 connector slots are included. The new console is backward compatible with Wii games and Wii accessories.

Update 2 :

Here is a video showing some of the features the new controller has, developer interviews and few of the launch titles :