Does your rain barrel sit higher than your raised bed? If not, are you planning on using a pump, to pump the water out of the barrel? What are you growing?
If your barrel is not higher than the bed, you could maybe use some rain barrel soaker hose. If you are pumping the water, you could use any form of drip irrigation.

There are many different drip system parts to look into. As twolips stated, it depends on where your rain barrel sits in relation to the area you will be watering.

Here is a link that might be useful: drip irrigation