As reported Nintendo announced a new DS today with the Nintendo DSi. The Nintendo DSi will launch in Japan on November 1st and in other countries in 2009. That is why all the marketing material for the Nintendo DSi is in Japanese at the moment.
Nintendo published a promotion video for the DSi that shows the new version in action and highlights upcoming DSi titles. One mystery accessory (see screen grab on the right) is also shown in this video). The DSi accessory looks like a remote control.

I could not find a description of this thing yet. If you know what it is please email me. Update: It is a Pedometer.

See the Nintendo DSi video here. See also the Nintendo DSi product page (Japanese).

The Nintendo DSi features a larger 3.25 inch LCD display and as far as I can see, two integrated cameras. There is one on the inside for self portraits and one on the outside cover. Nintendo has now integrated a music player in the Nintendo DSi that plays tracks from SD cards.
More details in this earlier DSi news story.