I quite like how Short Track UK run it. Short track (every full-size bike), Thunderbikes (air-cooled framers and street-bike based racers), Mini Bikes (adults on tiddlers), Juniors. Huge classes and the fastest guy wins.
This Lodi Class list was found on Poppawheelie by J-W Dutch Brother. He particularly liked the Beer Belly Class. We'd have a good go at filling that one in the UK. G