If the warning light is on that usually means that one of the sensors has been triggered. As Dudesky mentioned, there is one front and one rear. You would need to inspect both sets of pads to determine which need replacing.
When installing new brake pads (and a new sensor) you will want to either resurface/turn or replace your rotors. The ceramic pad suggestion is a good one. I run PBR Metal Masters on my 325. Minimal dust and good performance.