1963 Fiat 500 about 40 mpg (driven in 1978)
1968 VW Bug about 18 mpg (driven in 1982)
1972 Citroen GS about 27 mpg (driven in 1984)
1982 VW Passat about 26 mpg (driven in 1989)
1973 MGB-GT about 25 mpg (driven in early 90's)
1998 Subaru Outback Wagon about 25 mpg (driven 98-02)
2003 MINI Cooper S about 25 mpg (driven 03-05)
2005 Prius II about 47.5 mpg (since Jan 05).

So, started at 40 mpg, rapidly dropped to the mid-20's and stayed there until the Prius!