Nintendo's E3 press conference, where the final Wii U specs will be revealed, hopefully alongside a price and release date and launch titles will air on two TV channels in the US, Viacom owned MTV2 and Spike TV. Apparently the broadcast will be commercial free, but another way to look at it (and probably a more accurate way at looking at it) is that Nintendo are paying Viacom (or just giving them free access to fully produced materials) to air what is pretty much an orchestrated infomercial aimed at gamers (hey, we still love you Reggie, but it is what is). The press conference will also air on Facebook and Nintendo.com.
Nintendo's press conference is the third one of the three major ones and starts at 9:00 am (PST) on June 5 (that's 5:00pm UK time).