The 'official' 17" wheel standard is 7J ET38 with 205/40 tyres. However, as you rightly point out, there are variations on this theme - I currently run on genuine Audi TT wheels which are 7.5J ET32 with 215/40 tyres.
Spike is right though, you must be careful of rubbing on the ABS sensor wire - there has been a technical bulletin issued about this and later cars are pre-modified.
The ideal would be 225/45 tyres on 17" wheels, but these will not physically fit in to the arches. 205/45 does go, but you sacrifice rim protection which is why I've opted for the 215/40 option - adequate protection, improved ride comfort (still harsh though) and decent looks and handling.
Cheers,
Mike