Measuring the distances between vertices on graphs is one of the most fundamental components in network analysis. Since finding shortest paths requires traversing the graph, it is challenging to obtain distance information on large graphs very quickly. In this work, we present a preprocessing algorithm that is able to create landmark based distance sketches efficiently, with strong theoretical guarantees. When evaluated on a diverse set of social and information networks, our algorithm significantly improves over existing approaches by reducing the number of landmarks stored, preprocessing time, or stretch of the estimated distances. On Erdos-Renyi graphs and random power law graphs with degree distribution exponent 2 < β < 3, our algorithm outputs an exact distance data structure with space between Θ(n5/4) and Θ(n3/2) depending on the value of β, where n is the number of vertices. We complement the algorithm with tight lower bounds for Erdos-Renyi graphs and the case when β is close to two.