A 60's series 2 Lambretta. Light weight, so easy on the back and knees, and pretty simple.
Unfortunately many owners here in UK were more concerned with flash paint than the mechanicals, so some horrors are around. Some sharks swim in those waters too, so extra caution if shelling out for an import - even if the picture in ebay looks shiney!
Like any other mechanical device, careful selection and matching of parts is essential. They can be made reliable, but people often do expect too much of a 60 year old shopping trolley.
There is a 100mph Lambretta club. This summer a couple of folks got over the ton terminal - one over 104mph, on the standing mile. On road legal bikes, with 10" wheels (no road legal tyres in this size are rated for over 93mph).
I use MBD up in Yorkshire, excellent. Mark has done a lot of development over the years and produces first class bits which keep a lot of bikes on the road, safely.
Couple of fora to browse
http://scooterotica.org/forum/
http://www.forums.ilambretta.com/index.php
I had a Durkopp for a while back in the 60's, typical German machine of the time, pig ugly but the engineering and build quality were fantastic. Several others like the Heinkel Tourist was apparently even better. I swopped out to a Lambretta because I was even more shallow then and bought it on looks alone. Plus my mum would sign the hire purchase. She thought I would be safer going to uni on a new scooter. I wanted a proper bike
There were about 50 British built scooter makers. Most were horrid, with BSA and Triumph leading the charge.