You can get 17 and 18 inch, have seen some 20 inch ones on an A8 as well. Plus loads of different offsets and widths, hence it's a minefield if you are trying to buy some on eBay
If you were to buy 18" genuine's in 5x100 then im sure there will only be one offset et33 if I remember correctly? Im pretty sure only the TT and A3 have the 5x100 stud pattern
Cheap in need of a refurb!
Genuine Audi TT 18" RS4 Alloys on eBay (end time 06-Sep-10 18:31:33 BST)
Not so cheap in good nick with tyres
AUDI TT GENUINE ALLOYS IN EXCELLENT USED CONDITION. on eBay (end time 11-Sep-10 19:00:05 BST)