How to wake up computer in standby mode?

When I push the sleep button on my keyboard, my laptop (running windows XP) goes into standby mode. However, to wake the laptop up, I can't push the sleep button again, instead I have to open the lid and push the power button. Is there any special way to make the laptop come out of standby mode by pushing a key on the keyboard, or anything other than opening up the lid and pushing that power button?
The reason I ask is because the laptop will have something on it so opening the lid will be very inconvenient.