I've been pondering on this one as well. The major difference that I can identify easily is the placement of the indicators on the side, the facelift models are in front of the wheel arch apposed to the near the wing mirror. Also there are some rear lights on the side on the rear bumper, I thought they were reflectors but they should light up. (Cheers Ash!)
I think and don't quote me that the TTs get UK type brakes, the NAs don't.
On my facelift I have five dials on the dash, Revs, Speedo, temp, battery and fuel.
I'm sure everyone else will come up with some technical stuff but there are the cosmetic differences that I've come across.