I am slightly biased since my favorites were the onces that were applied to social networks:
1) A social network caught in the Web.
2) Evaluating similarity measures: a large-scale study in the orkut social network.
I also loved this other research paper I read yesterday on collaborative intelligence, "Item-based Collaborative Filtering Recommendation Algorithms" available at http://www.paulperry.net/notes/cf.asp
Limits of Anti-Phishing: http://www.w3.org/2005/Security/usability-ws/presentations/37-google
How to Design a Good API: http://lcsd05.cs.tamu.edu/slides/keynote.pdf