Richard Jones' Garbage Collection Page
Richard Jones wrote Garbage Collection: Algorithms for Automatic Dynamic Memory Management", the first English book concerned solely with garbage collection. Garbage collection page has an FAQ, and a large bibliography.
http://www.cs.kent.ac.uk/people/staff/rej/gc.html

An Introduction to Garbage Collection, Part I
Presents an introduction to garbage collection, presenting the subject in enough detail to show the various tradeoffs and advantages between various techniques and what goes on under the hood in a typical garbage collector.
http://icu.sourceforge.net/docs/papers/cpp_report/an_introduction_to_garbage_collection_part_i.html

Paul Wilson's Garbage Collection Archive
A collection of papers on garbage collection, memory allocation, and the like from the OOPS Research Group at the University of Texas at Austin. Includes papers from the OOPSLA Workshops on Garbage Collection in 1990, 1991, and 1993.
ftp://ftp.cs.utexas.edu/pub/garbage/

A garbage collector for C/C++ (Hans Boehm)
Hans Boehm's page on the widely used Boehm-Demers-Weiser conservative garbage collector for C/C++. The Boehm-Demers-Weiser conservative garbage collector can be used as a garbage collecting replacement for C malloc or C++ new. It is also used by a number of programming language implementations that use C as intermediate code.
http://www.hpl.hp.com/personal/Hans_Boehm/gc/

Garbage Collection: Automatic Memory Management in the Microsoft .NET Framework
Explains how resources are allocated and managed, then gives a description of how the garbage collection algorithm works. Also discussed are the way resources can clean up properly when the garbage collector decides to free a resource's memory and how to force an object to clean up when it is freed. By Jeffrey Richter, MSDN Magazine.
http://msdn.microsoft.com/msdnmag/issues/1100/GCI/default.aspx

Garbage Collection: Automatic Memory Management in the Microsoft .NET Framework, Part 2
Explains strong and weak object references that help to manage memory for large objects, as well as object generations and how they improve performance. In addition, the use of methods and properties for controlling garbage collection, resources for monitoring collection performance, and garbage collection for multithreaded applications are covered. By Jeffrey Richter, MSDN Magazine.
http://msdn.microsoft.com/msdnmag/issues/1200/GCI2/default.aspx

An Introduction to Garbage Collection, Part II
Show how garbage collection works and what it actually costs.
http://icu.sourceforge.net/docs/papers/cpp_report/an_introduction_to_garbage_collection_part_ii.html

Garbage Man
Garbage Man is the premiere junk e-mail filter for America Online. Take out your junk e-mail today!
http://www.waveop.com/garbageman/index.htm

Hans J. Boehm
HP Labs is the central research lab for Hewlett-Packard.
http://www.hpl.hp.com/personal/Hans_Boehm/

Wikipedia: Garbage Collection (Computer Science)
Online encyclopedia article.
http://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29