The Europcar First Card seems to really make a difference at FRA Airport:

For 2x CPMR I got a BMW 320ad and a Mercedes E200, both with built-in Navigation.

Last CLMR: brand-new Merceded C220 (Diesel) > nice ride & voice input for the navigation .

Last 2x IDAR: a Mercedes CLS 320 (Diesel)... not too bad either & one BMW 530ad Touring (albeit with 210km/h limit due to wintertyres) - And taking advantage of the lufthansa triple mile offer as well (Happy Code: LH0704EXMG; for Intermediate size rentals and above, valid until 30-June 2007).