#mymiddleware.py
class RedirectToNoSlash(object):
    def process_request(self,request):
        if '/admin' not in request.path and request.path != '/':
            if request.path[-1] == '/':
                return HttpResponsePermanentRedirect(request.path[:-1]) 

#settings.py
MIDDLEWARE_CLASSES = (
    'mymiddleware.RedirectToNoSlash',
    ...            
)

#Make sure its the first middleware, or its before any url manipulating middleware such as CommonMiddleware.