On the configurator there is a standard features list for each model - you'll find it in the top left hand corner, just click and read/download for each model. From memory the differences are:
Engine - B gets a 2.0L turbocharged, S gets a 2.5L VTG turbocharger. This of course means that power output and torque differs for each model
Brakes - Z gets bigger brakes with Red calipers
Wheels - B gets 18" rims as standard, the S gets 19" wheels
Exhaust - B gets a large oval exhaust tip, S gets two circular ones
Interior - the S gets extra leather on the centre cubby hole and on the door handles plus 'sportier' looking pedals.
There may be one or two things i've missed but I think that's about it. Also remember that standard equipment will vary from country to country - for eg. in some countries climate control is optional while it's standard in others so pays to make sure you are looking at country specific information, which is why country specific spec sheets from the configurator are your best starting point.