Big companies are hoping to marry their brands to gays and lesbians this weekend — about 20,000 of them. In the first days after the presidential election — in which gay marriage proved to be a pivotal issue — the nation's biggest exposition on homosexual life is setting attendance records. Booths for exhibitors are also sold out for the first time at the Javits Center, which since 1999 has hosted Gay Life Expo, one of the center's liveliest trade shows. Companies ranging from Citigroup and American Express to Jet Blue and J.P. Morgan Chase are hawking their offerings to the...