stock (most are hollow, see wall thickness):
TT-RS quattro: 22 mm solid / 18.5 x 2.5 mm
A3 Ambition/S-Line: 22,5 x 3,5 / 20,7 x 2,8
Golf V GTI: 23,6 x 3,5 / 21,7 x 3,0
Golf V R32: 22,0 solid / 21,7 x 3,0 (4-motion)
Golf VI GTI: 23,6 x 3,5 / 21,7 x 3,0 PR-0BF or 21,7 x 3,6 PR-0BM (DCC?)
Golf VI R: 22,0 solid / 21,7 x 3,6 (4-motion)
Scirocco R: 23,6 x 3,5 / 21,7 x 3,6
Touran 170 PS: 23,0 solid / 21,7 x 3,0
Passat R36: 23,6 solid / 21,7 x 3,6 (4-motion)
Sharan 2011 on: 24.0 mm solid / 20.0 mm solid
after market (almost all are solid):
H&R TT Quattro: 24 / 22 mm inkl. TT-RS
H&R 'small': 26 / 22 mm
Eibach AntiRoll: 26 / 23 mm
KW clubsport: 26 / 23 mm (made by Eibach)
VW Racing: 26 / 23 mm (made by Eibach)
H&R 'big': 28 / 24 mm (there's also 28 mm rear bar at AWE)
H&R 4-motion/Quattro: 25 / 25 mm
Autotech: 25 / 25 mm (tube/hollow)
Whiteline: 24 / 24 mm (3-way adjustable)
Neuspeed: 25 / 25 mm (tube/hollow; also 28 mm rear avail.)
Hotchkis: 27 / 27 mm (tube/hollow)
APR: 27 / 27 mm (tube/hollow; made by Hotchkis)
BSH: -- / 27 mm (3-way) rear only