Yoga Shakti with Shiva Rea. Comprehensive but user-friendly, reasonably challenging but accessible to a variety of levels, Yoga Shakti is inarguably one of the best yoga products on the market -- no small achievement when one considers just how many of them there are. Instructor-creator Shiva Rea, a California-based yogi of considerable international renown, specializes in vinyasa yoga (a vinyasa is essentially a series of flowing, connected poses, incorporating breath and movement and cultivating heat, strength, flexibility, and balance). Four complete practices are presented, ranging in length from 42 to 85 minutes and including Basic Flow (for beginners), two more vigorous Solar Flow sequences, and a Lunar Flow sequence falling somewhere in the middle in terms of degree of difficulty; familiar poses like sun salutations, forward bends, lunges, twists, and inversions are featured, although Rea adds many of her own touches (such as the four ''dancing warrior'' sections, sun salutation variations designed for intermediate users and focusing on hips, backbends, and so on), and there are also sections devoted to pranayama (breathing exercises) and meditation. Yoga Shakti also has the popular ''yoga matrix,'' which allows users to customize and program their own workouts. Also contains a bonus disc -- interviews, additional instruction, travel footage (India and the Maldive Islands), and more.