Linqpad - http://www.linqpad.net/
Reflector - http://www.red-gate.com/products/reflector/
Pixie - http://www.nattyware.com/pixie.php
Notepad2 - http://sourceforge.net/projects/notepad2/
VirtualCloneDrive - http://www.slysoft.com/en/virtual-clonedrive.html
Paint.NET - http://www.getpaint.net/
ProcMonitor - http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx
TCPView - http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx
Expresso - http://www.ultrapico.com/Expresso.htm
WSCF - http://www.thinktecture.com/Resources/Software/WSContractFirst/default.html
EasyDebugWindowsService - http://blog.decarufel.net/2009/01/debugging-windows-service-without.html
Log4Net - http://logging.apache.org/log4net/index.html
Rhino Mocks - http://ayende.com/projects/rhino-mocks.aspx