rundll32.exe powrprof.dll,SetSuspendState 0,1,0

But, if you first run this command in an elevated cmd window (that your ran by right clicking Command Prompt, and clicking "Run as administrator"), the above command will suspend your computer instead of hybernate it.

powercfg -hibernate off

If anyone reading this doesn't know the difference between suspend and hybernate:

• Suspend does not turn off your computer. It puts the computer and all peripherals on a low power consumption mode. If the battery runs out or the computer turns off for some reason, the current session and unsaved changes will be lost.

• Hibernate saves the state of your computer to the hard disk and completely powers off. When resuming, the saved state is restored to RAM.

I found that here.