A specimen Roach, Perch or Barbel would do for me. I tend to fish specifically for these fish at different times of the year on different venues.
To actually be targeting one of these species and to catch a good sized example is very satisfying.
It's all a matter of perspective, in July I caught a Roach over 1.5lb (I didn't actually weigh it because I don't carry scales). I'm extremely happy with that fish, but being under 2lb in weight, it wouldn't be considered a specimen by most people.
In the Autumn I will be out trying to catch a nice Perch or two, if I catch anything 3lb or over I will be more than satisfied.