An interesting WWW 2006 workshop paper, "Propagating Trust and Distrust to Demote Web Spam", surveys and expands on the ground covered by TrustRank.
The paper starts by describing TrustRank and some of the related work. It then talks about a similar mechanism for propagating distrust -- working from a blacklist of known spam sites instead of a whitelist of known good sites -- which they refer to as "BadRank". They end by experimenting with a few alternative methods of propagating both trust and distrust through the link graph that may have better performance than TrustRank.
A worthwhile read if you have any interest PageRank, TrustRank, and the efforts to fight off web spam.