Johnny Jet was supposed to fly out today, but his flight was delayed. Fortunately, I had alerts from his airline, and TripIt Pro in order to get notified. He was also able to rebook through Dallas in Business Class for almost the cost of coach. He used miles, though. Johnny also recommends renting your car through Costco Travel. The prices will drop as you get closer to your travel date, and you can always cancel and rebook. But stay away from the prepay guarantee. That locks your rate in.
Also, when travelling in Europe, rent a small car. In fact, don't get a car period. Parking is always an issue. It's also very stressful to rent internationally. Trains in Europe are more efficient anyway.