I owned a 2000 Jetta TDI for about 4 years (chipped for 2 years) and I averaged around 45mpg lifetime, with my best mpg for 1 tank of gas topping 53mpg.
My current car (2005 Volvo S40 T5) has averaged almost 24mpg lifetime and just over 30mpg for its best tank. Not bad, but it makes me miss my old Jetta sometimes.
And lately I've been commuting on my motorcycle (2006 Yamaha FZ6) and have been getting around 160 miles on one tank, so that's around 48/49mpg... not bad for something that can do 0-60 in under 4 seconds.