GayWeddings.com - this site is great in that it features an extensive online boutique where you can find two-bride and two-groom themed invitations, guest book and other items for sale. They also have an online vendor directory and some planning tips. This site is the oldest of its kind.
SoYoureEnGAYged.com - I love this site because any vendor you hire from their vendor directory has been screened to be gay friendly and must have inclusive language on their website and in their marketing materials. That is the #1 thing the separates this site from the rest. You know you'll be in good hands. Also check out real wedding blogging by engaged couples and featured real weddings.
What online resource have you found to be most helpful when planning your gay wedding?