The most highly rated razor for head-shaving is the HeadBlade, according to AskMen and Grooming Lounge. The system fits neatly in one hand, with a suspension system designed specifically for head use. With wheels on one end, it's flexible and requires very little effort.
Reviewers at About.com and The Bald Nation also give the HeadBlade very favorable reviews; both reviewers indicate their intention to continue using it. It uses much longer strokes and less pressure than a traditional razor, leading to fewer ingrown hairs and less irritation. Associated products, also well-reviewed, include HeadWash, HeadSlick Shave Cream, HeadShed Exfoliating Scrub, HeadShade Sunscreen, ClearHead and HeadLube Moisturizing Lotion.