For the first time in Gallup's tracking of the issue, a majority of Americans (53%) believe same-sex marriage should be recognized by the law as valid, with the same rights as traditional marriages. The increase since last year came exclusively among political independents and Democrats. Republicans' views did not change.
To be specific, Gallup says Democrats who approve went from 56% to 69%, Independents from 49% to 59%, and Republicans stayed at 28%. The results broken down by ideological leaning are similar: liberals went from 70% to 78%, moderates from 56% to 65%, and conservatives from 25% to 28%.
(h/t: Jon Terbush/TPM, who has links to other relevant polls, as well)