There are others around:
One at Bourne airfield - Rural Flying Corps. 7 miles to the west of the city centre. Never been there myself, but the gliders at Grandsen seem to ignore the ATC zone on a regular basis and gravitate to it.
Conington - South of Peterborough, nice and cheap.
Sibson Peterborough.
The main ones at the Cambridge city airport are obvious candidates, although watch out for the landing fee charges at one school - it could get expensive with touch and go's.
I suppose it depends if you have your own transport or not, or else you may be stuck to Cambridge based schools.