CarvingPumpkins.com: The Pumpkin Wizard is a terrific resource for learning how to carve 3-color pumpkins. This site also has members-only patterns and an online storefront for buying pumpkin carving supplies. Specific page to access for carving a pumpkin with transfer paper is here.
CarvingPumpkins.com Q&A Board: The Q&A board serves as a pumpkin carving community of practice. There you will find pumpkin carvers of all skill levels sharing advice on carving real and fake pumpkins and pattern making. You will also find a nice group of pattern makers there, many of which are willing to share their patterns.
Halloween Pumpkins: There is a decent tutorial here that can give you the basics of carving
Villafane Studios: Ray Villafane is an awesome professional artist who creates the most impressive 3D pumpkin sculpts. I am still a novice at this type of carving, but found his tutorial very illuminating. You also can check out his most awesome carvings here. For other pumpkin sculpts, check out PumpkinGutter.com.