I am picking up a car in Milan and doing a 21 day loop up through Germany and Austria. Reading the books, there is a discussion of a environmental badge needed in Germany and a similar voucher in Austria. I have seen conflicting information on where these can be obtained and how easy it is. Has anyone picked up a rental outside of Germany and acquired these? Any input would be appreciated.
Funny that the German environmental badge (for driving into the centers of larger cities) seems to be not often discussed. There's info and online ordering at http://www.umwelt-plakette.de/englis_informations.php, but you can't order ahead without the details of the specific car. Rick's Germany book mentions buying it at a border station or gas station, with the car rental paperwork in hand; I have not heard any reports to the contrary.
If the car doesn't already have the Austrian highway tax vignette valid for the year, then you'd again have to buy one at a border station or large gas station near a border. You are pretty likely to drive on some roads where this is required.
I don't know the specifics of getting an Umweltplakette for a foreign-registered car, but you may not even need one. They are only required for driving within the limits of relatively large cities. You would need one if you plan to take the car into Munich (which I wouldn't particularly recommend anyway).
The Austrian vignette is different. It is required for driving on the Austrian Autobahn network. You can buy one at the border or at petrol station near the border.