I have the VAG-COM that I bought from http://www.ross-tech.com . The UI is pretty bad (think bad shareware) but it works.

Here's a list of people willing to let you use their VAG-COM. (A 6 pack or something similar is the typical gesture of thanks.)

http://www.steve-hall.com/cgi-bin/VAG-Locator.pl

Find the appropriate forum for your car (probably at www.audiworld.com or www.vwvortex.com) for discussions on what can be done. Common things are:

change power lock behavior
window up/down from keyfob
allow fog lights to be used with high beams
put auto tranny in sport mode
clear check engine light (often evidence of engine mods)

On my Allroad you can change the air suspension ride hight for when you really want to pimp it out.