The tables below, list some of Google's eclectic mix of open source luminaries grouped by project.
No doubt I've forgotten some, so don't hesitate to contact me with corrections/additions.

Python
Guido Van Rossum Python creator
Alex Martelli Python Cookbook, ...
Jeremy Hylton Zope
Neal Norwitz PyChecker
Collin Winter functional
Mark Pilgrim Books, libs
Anthony Baxter release manager, libs
Linux Kernel
Andrew Morton  
Martin Bligh  
Daniel Phillips  
Ross Biro  
Paul Menage  
Richard Gooch  
Subversion (Google Code)
Ben Collins-Sussman  
Brian W. Fitzpatrick  
Karl Fogel Also SCM books
Daniel Berlin  
Greg Stein  
Peter Lundblad  
Eric Gillespie  
Mozilla / Chromium
Ben Goodger  
Darin Fisher  
Brian Ryner  
Fritz Schneider  
Mike Pinkerton  
Aaron Boodman GreaseMonkey
Eric Seidel WebKit
Community relations
Chris DiBona from Slashdot
Andy Hertzfeld from Apple, Eazel
Jason Robbins tigris.org
Zaheda Bhorat from Openoffice
Zach Brown Kernel Traffic
Misc
Rob Pike UNIX, UTF8
Ken Thompson UNIX, UTF8
Russ Cox Plan9
Eric Grosse Plan9, Netlib
Peter Weinberger aWk
Stuart Feldman Make
Vint Cerf TCP/IP
Udi Manber Glimpse
Raph Levien Gimp, Ghostscript, ...
Peter Mattis Gimp
Spencer Kimball Gimp, Gnutella
Josh MacDonald PRCS, xdelta, GTK+
Sean Egan Pidgin
Jon Trowbridge Gnome/beagle
Mikal Still ImageMagick, ...
Dan Kegel Wine, crosstool, ...
Ian Lance Taylor GNU toolchain
Diego Novillo GCC optimization
Glen Murphy Browser stuff
Joe Gregorio Atom, python libs
Han-Wen Nienhuys Lilypond
Bruno Albuquerque openBFS
T. V. Raman Emacspeak
Murray Stokely FreeBSD core team
Nik Clayton FreeBSD docs, ...
Amit Singh OS X system stuff
Frank Mayhar UNIX kernel stuff
Ben Laurie openssl, apache-ssl
Neil Fraser diff-match-patch, ...
Tim Hockin linux system utils
Adam Langley ObsTCP
Michal Zalewski security tools
James Youngman findutils, ...
Brad Fitzpatrick web server tools
Robert Love Gnome/kernel/books
Jean-loup Gailly zlib
Bram Moolenaar Vim
Jeremy Allison Samba
Eric Schmidt (CEO) Lex

Gradually Google is becoming less secretive, especially so since 2005/2006. Consequently it can attract high profile people from the open source community, on whose technologies it depends so much. As well as employing those above and many others involved in open source, it has begun to interact more with the community. For example Google has started to release internal tools, provide an open source project hosting service and runs the very cool Summer of Code initiative. These are definitely not trivial undertakings. For instance Google has spent the following on the Summer of Code project:

Project Students Amount
SoC 2005 400 $2.0M
SoC 2006 600 $3.0M
SoC 2007 900 $4.5M
SoC 2008 1125 $5.6M
SoC 2009 1000 $5.0M

This is money well spent as they get better open source software, kudos from the community and also get an early view of blossoming open source stars. Other notable Google hackers not directly involved in open source are:

Name Previous experience
Peter Norvig NASA
Andrew Moore Carnegie Mellon
Steve Lawrence CiteSeer
Douwe Osinga Google hacks
Mike Burrows altavista, Microsoft (spam research)
Adam Bosworth Microsoft: access, IE
Mark Lucovsky Microsoft: NT, .NET
David Hanson Microsoft: compiler research
Martin Taylor Microsoft: linux strategist, VP of live
李开复 (Kai-Fu Lee) Microsoft: speech research
Joe Beda Microsoft: Avalon, IE
© Jun 5 2008