Web aggregators select and present content culled from multiple sources, playing an important taste-making and promotional role. Larger aggregators are starting to compete with mainstream news sources but a new class of niche and do-it-yourself aggregators are organizing around specific interests. Niche aggregators harness the power of the internet to build communities previously separated by geography or institutional inertia. These micro-communities serve a trend-setting role. Understanding their operation is critical for those wanting to understand or predict cultural change and for those who want to harness the power of the long tail by catering to niches.