In reply to esoteric:
Church Beck at Coniston is short but quite fun, and afterwards you can do Levers Water Beck or Low Water Beck. I haven't done Low Water Beck but think it's more of an 'upwards' scramble (not so many pools) if that makes sense? And I've only done Levers Water Beck in high water levels which made it rather interesting, possibly not so good in drier weather.
Honister Gill from Seatoller is quite entertaining, ideal for an hour or so on a summer evening.
The Esk Gorge is the classic though.