Fastest way to reproduce a Blue Screen of Death (BSOD)?

There is in fact a developer tool built into most versions of Windows to generate a BSOD on command. Here's how you cause it in Windows 7 on either a USB or PS/2 keyboard (I believe it is the same for XP/Vista on USB even though this article doesn't say so, I may be mistaken though):

You must ensure the following three settings before the keyboard can cause a system crash:

If you wish a crash dump file to be written, you must enable such dump files, choose the path and file name, and select the size of the dump file. For more information, see Enabling a Kernel-Mode Dump File.

With PS/2 keyboards, you must enable the keyboard-initiated crash in the registry. In the registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\i8042prt\Parameters, create a value named CrashOnCtrlScroll, and set it equal to a REG_DWORD value of 0x01.

With USB keyboards, you must enable the keyboard-initiated crash in the registry. In the registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\kbdhid\Parameters, create a value named CrashOnCtrlScroll, and set it equal to a REG_DWORD value of 0x01.

You must restart the system for these settings to take effect.

After this is completed, the keyboard crash can be initiated by using the following hotkey sequence: Hold down the rightmost CTRL key, and press the SCROLL LOCK key twice.

The system then calls KeBugCheck and issues bug check 0xE2 (MANUALLY_INITIATED_CRASH). Unless crash dumps have been disabled, a crash dump file is written at this point.

If a kernel debugger is attached to the crashed machine, the machine will break into the kernel debugger after the crash dump file has been written.

This is an old documented technique. Should work at least up to Vista:

Find in regedit:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\i8042prt\Parameters\

Create a DWORD key named CrashOnCtrlScroll and set it's value to 1.

...

To generate a BSOD, hold the right CTRL and press ScrollLock twice.

You can enable manually initiated crashes by performing these registry changes.

If your BIOS can switch your system's hard drive adapter between native SATA and legacy ATA mode (and possibly IRRT), switching to a different mode Windows was installed in will usually produce a BOOT_VOLUME_INACCESSIBLE error. I'm pretty sure disabling ACPI (if possible on your BIOS) when Windows was installed with ACPI enabled will also result in a bluescreen on boot.

Killing winlogon.exe using Sysinternal's Process Explorer produces a blue screen, but it's not the traditional "A problem has been detected and Windows has been shutdown to protect your computer..." screen.

This may also interest you - BlueScreen Screen Saver from Sysinternals.