Simulating a BlueScreen
You can configure a machine to crash on a keystroke (Ctrl-ScrollLock)
Since it appears that there are times when that won't work on some systems with USB keyboards, you can also get the Debugging Tools for Windows, install the kernel debugger, and use the ".crash" command to force a bugcheck.
In order to cause a BSOD, a driver running in kernel mode needs to cause it. If you really want to do this, you can write a driver which exposes KeBugCheck to usermode.
http://msdn.microsoft.com/en-us/library/ms801640.aspx
Thanks to Andrew below for pointing this utility out: