If you're attending the San Diego Comic-Con this year from July 21-24, you'll be able to get your hands on The Legend of Zelda: Skyward Sword. I played it at last year's E3, and then the newer demo at this year's E3, but this is the first time the general public will be able to play the game. If that's not your cup of tea, you'll also be able to play the 3DS games Super Mario, Mario Kart, Kid Icarus: Uprising, Star Fox 64 3D, and more. In fact, they're going to have Shinobi, which they didn't have in the 3DS area at E3. (At least, not that I saw!)
In addition to the 3DS and Wii games you can demo, there will be a couple of events going on. To celebrate Zelda's 25th anniversary, Nintendo has commissioned an artist to create an elaborate chalk drawing, and he'll be working on it over the course of the con, so you can check back periodically to see how it's coming. (I won't be there, so I hope to see pictures of the final result!) There will also be a special Pokémon meet-up on July 21 from 4-6pm at the Nintendo Gaming Lounge. Pokéfans will be able to battle and trade with Pokémon Black and White as well as trade Pokémon data for the 3DS app Pokédex 3D. There will also be plenty of giveaways for Pokémon and other Nintendo properties. Also, as I can attest from PAX East and E3, these kinds of places are the absolute best to StreetPass folks!