I am a loyal Caffeine user, but if for whatever reason that program does not convince you and you want an alternative, InsomniaX will allow you to enjoy the same or more benefits at the same price of zero euros.
Compiled to work on PowerPC and Intel, This small program is housed in our menu bar as a Menulet and allows us to disable the Mac's sleep mode, as well as force it and turn off the screen.
Little more to say about a simple utility but that everyone should have on their Mac to use at certain times, for example, when we let something go down and we do not want our power management program to put the Mac into Sleep mode.
Link | InsomniaX