The document discusses several algorithms for reputation and ranking systems on graphs, including blogs and social networks. It begins with discussing the Sybil attack and SybilGuard for detecting such attacks. It then covers algorithms for ranking blogs like BlogRank, B2Rank, and EigenRumor that take into account factors like blog activity, links, and comments. MailRank and TrustRank are discussed for using reputation propagation and spam scores to detect spam. The challenges of building measurable and dynamic reputation systems that avoid an arms race are also summarized.