Here's a link to VW and Audi OEM wheels that fit our Touaregs.
http://www.myturbodiesel.com/1000q/wheels/touareg-wheels-gallery.htm
The pros and cons of the normally available rims has been discussed here extensively, but in a nutshell, and keeping with a nominal stock tire diameter of just over 29":
The smaller diameter rims (17 and 18 inch) will give you a higher sidewall, therefore a more comfortable ride, a greater selection of tires at much more reasonable prices, and the ability to use snow chains on some of the stock tire sizes. These are favoured sizes of people driving in winter conditions, and of course, off road/back road conditions where reducing the tire air pressure will greatly increase traction, in a snow/mud/sand conditions.
The larger diameter (19 and 20 inch) rims are aimed at improving extreme high speed handling, by making the tire sidewall shorter and reducing sidewall flex. Very common on track cars and high end autobahn cruisers. This comes at the increased cost of tires, a harsher ride, and reduced selection of tires. Of course, the larger rims have the "bling" racer appearance factor, which is currently in vogue.
The key thing is to match your wheels and tires to your particular driving requirements, Touaregs are very, VERY, capable vehicles, just don't be let down by an unsuitable wheel/tire combination, because, as they say, "It's all about how the rubber meets the road!".