PostgreSQL Wiki
(documentation, how-tos, and tips 'n' tricks related to PostgreSQL [external])

Architecture of a Database System
(Hellerstein/Stonebraker/Hamilton, Foundations and Trends in Databases, 2007 [external])

Interview with Bruce Lindsay
(Entertaining and insightful comments from a database pioneer)

MVCC Unmasked
(Bruce Momjian, slides from a 2011 presentation)

On the Analysis of Indexing Schemes
(Hellerstein/Koutsoupias/Papadimitriou, ACM PODS Conference 1997)

Perfect Hashing for Data Management Applications
(Botelho/Pagh/Ziviani, CoRR 2007)

A Comparison of Approaches to Large-Scale Data Analysis
(Pavlo/Paulson/Rasin/Abadi/DeWitt/Madden/Stonebraker, SIGMOD 2009)

Early Hash Join: A Configurable Algorithm for ...
(Lawrence, VLDB 2005)

Exploiting Join Cardinality for Faster Hash Joins
(Henderson/Cutt/Lawrence, SAC 2009)

Using intrinsic data skew to improve hash join performance
(Cutt/Lawrence, Information Systems 2009)

Inside the PostgreSQL Buffer Cache
(Greg Smith, Consultant for 2ndQuadrant, 2008)

Multiple Buffer Pools and Dynamic Resizing of Buffer Pools in PostgreSQL
(Nailah Ogeer, Masters Thesis, Queen's University, Canada, 2004)

More to come ...