I'm currently researching renting a car in Munich for a week this August.
I was only paying attention to prices of convertibles ;) and these sites had the best offers:
- http://www.economycarrentals.com/ (the one I booked!)
- http://travelsupermarket.com
- http://www.ca.kayak.com/cars#/MUC-a14057/2013-08-06/2013-08-13
- http://www.arguscarhire.com
- http://www.autoeurope.com/
- Autoeurope has a VISA promotion right now… after calling with this they gave me ~8% off
- http://usa.visa.com/personal/discounts/detail/AutoEurope_13_S13/vro_details.jsp?offerName=AutoEurope_13_S13&offerId=38772&pageId=197
Note that CDW insurance is complicated. The rental I ended up booking via economycarrentals.com is "all inclusive", but still has a 1050€ deductible. For an extra $50, I could have bought zero deductible for the week.
Also, this might be useful: files.meetup.com/992386/Renting%20cars%20in%20Europe.docx ("How to Rent a Car in Europe By Rick Steves")
Good luck!