Rosenthol Design: If you need graphic design–business cards, posters, invitations, etc–she’s the one to go with. She also helped design the look of Magic & Misadventures.
World of Walt: This excellent site offers Disney-related articles as well as a great forum for like-minded fans to chat. I’m a frequent commenter on the forums, occasional contributor of articles, and I’ve been a guest on The World of Walt Podcast: Make the Most of Your Walt Disney Vacation.
Disney Parks: If you need to make a reservation or get information on the parks, the official Disney Parks site is the place to go. Once you have your reservation, use My Disney Experience to further plan, make reservations, get Fastpasses, and more.