Which replacement break pads should I get?
 

The light saying my break pads need replacing soon came on a couple of days ago. My friend and I will probably change them ourselves since I don't imagine it'd be too hard. However, I don't know which pads to get. Are there different pads front and rear and do I need to get Greenstuff or Redstuff or whatever they're called?

The original OEM brake pads work great, no need to buy aftermarket unless you really cannot stand the dust.

Get the Axis deluxe pads if brake dust bothers you.
BMW X3 Products: Axxis brake pads, clutch delay valve (CDV), tires

Yes, they are different front and rear.

Lemans was suggesting the Axxis Deluxe pads.

Presume you know to replace the sensor (the one that caused the light to come on). It is a single-use switch, disposable. One on the front axle, one on the rear.

How long since the brake fluid was replaced? It is scheduled for every 24 months. Also check rotor condition. They aren't usually turned on a lathe, but simply replaced, if they are at the minimum thickness or if the surface finish is not great.

Just replaced the front pads and sensor with TRW...so far so good

I replaced mine to ceramic Euro Akebonos- AWesone - no brake dust in 2 weeks of use and stopping power is great.