We did use Luken Limousine on our way back to the airport for the trip three weeks ago. Website is
http://luken-limousine.com/
They were recommended somewhere on the board, but I can't find the topic now.
They have a secure online booking form and offer 20 percent off for online bookings of Sedans available at the moment.
They suggest a pickup time on the online booking form, but if you want to change that you can do that on the form - which we thankfully did, check in at the Lufthansa counter was a nightmare this time due to a cancelled flight before us.
The driver showed up right on time, the car (Sedan) was nice and roomy. No problem at all to get in with my crutches, and 5 large bags/suitcases and our carry on items fit in easily too.
Service was excellent, and we felt safe and comfortable all the time. I definitely recommend them, and they're already on my list of airport transportation back for 2010. *g*