For 3DS owners, Nyko has the Shock n' Rock cradle, which offers two times the battery life and four powered speakers, along with vibration feedback. The company is also showing off the Game Boost, an accessory that adds an extra hour or two of battery life. There's also the Power Grip, which supposedly adds three times the battery without removing the device's power.
Most extravagantly, there's the Play Clock for 3DS. A combination: charging dock, alarm clock and powered speaker system. There's also a line-in port for connecting your MP3 player of choice. It's actually pretty nifty, depending on what the final price ends up being.
Pricing and release dates are still unconfirmed for all the products, but all of the items should be available in time for the holidays.