Sorry to say but Donington isn't what it was. Wheatcroft Jr. has sold off an awful lot of cars in the last couple of years and given over one entire hall to his rather dull collection of military vehicles. Seeing as there are a whole heap of other guns'n'tanks museums out there (I live down the road from the Canadian national one...) this is a huge disappointment to me. Ok, so the old layout was a little haphazard and crowded, but at least the cars were there to look at.
Haynes is a good one, and although it has been quite a few years since I last went there I do remember enjoying it.
The Cars of the Stars museum (
http://www.carsofthestars.com/) was also a fun couple of hours if you happened to be in central Cumbria on a wet weekend, although sadly it appears that they are currently closed pending a move to new premises.
On two wheels there is of course the National Motorcycle Museum (
http://www.nationalmotorcyclemuseum.co.uk/museum/) near Birmingham airport. As someone only a little interested in 'bikes it is a little overwhelming but if you are of the two wheel tribe then it's unmissable as there are some ultra rare things stowed in there. Being of the age I am, the ****el-engined GP Nortons were definitely to be drooled over...
Anyway, hope that helps a little?