According to the official website, Nintendo will give a presentation at the 2006 Games Convention in Leipzig, Germany. The hour-long presentation, entitled "Wii prove our promise," will start at 10:15 a.m. on August 23rd. Last week, a rumor from Comic-Con mentioned that some Wii announcements at Leipzig, and Nintendo's presentation seems to corroborate those rumblings.
Nintendo has stated they would reveal launch details, including pricing, sometime in September. August 23 might be close enough for a revelation or two.