Here are some screen captures from various operating systems/window managers/desktop environments, some of which I used just a little longer than needed to take a screenshot.

Haiku R1 Alpha 1
IRIX 6.5
on an SGI O2
Mac OS X "Leopard"
Metisse on Mandriva One 2007
Windows Vista Beta 2
Fedora Core 5
Cool desktop switching with Compiz & Xgl on Ubuntu
Mac OS X "Tiger"
Fedora Core 1
LindowsLive! 4.5
Plan 9 Fourth Edition
Virtual PC on Windows XP
iTunes on Windows Server 2003
Epiphany in fullscreen mode
SuSE Linux 8.1 LiveEval
Knoppix 3.2
Recursive VNC trick
(Red Hat 8.0.94, KDE 3.1)
Gnome 2.0 & Metacity
(Red Hat's Bluecurve theme)
Gnome, Window Maker & nice transparent terminals
KDE 2.1.1
MacOS 7
Ximian Gnome 1.4 with Nautilus
Gnome & Window Maker
Gnome & Enlightenment with an Aqua theme
Window Maker
AfterStep and some important applications
Gnome & Enlightenment
AfterStep and XMMS
BeOS 5 Personal Edition
QNX Realtime Platform (Photon)
Windows 95 and Smalltalk
Windows 95 and Q3Radiant
Windows NT 4.0 and Smalltalk