Nintendo of America will have a presence at Comic-Con, trotting out voice-of-Mario Charles Martinet for autographs and unfortunate souls in Link and Mario suits to make their requisite appearances as well.
Comic-Con attendees are encouraged to deck themselves out as Nintendo characters to "increase their chances of winning swag" (Nintendo's words, not mine). Nintendo will be giving away oversized postcards each day as well as DS Lite systems and Nitendo DS software.
A DS Download Station will also be available to offer demos to DS owners at the show. Nintendo's booth is #2429; you can check them out July 19-20 and 22-23.