Blacktoft Sands RSPB reserve is very good in September for waders and the Marsh Harriers should be still around.
Blacktoft can be tricky because birds are often quite distant from the hides, although the marsh harriers do give a good show.
Other places that can be good for quick visits include:
Potteric Carr (near Doncaster) - good range of species, with a good hide overlooking feeders where you'll get cracking shots of great spotted woodpecker, jay etc.
Old Moor (near Barnsley) - good range of waterfowl and some waders, plus feeders which will have bullfinch, willow tit, tree sparrow, stock dove etc.
Fairburn Ings (near Castleford) - a good place for waterfowl (although it's slightly early for most of the best stuff), and kingfishers, plus a good feeding station for common passerines.
Filey Brigg - a good site for waders, including purple sandpiper, bar-tailed godwit, knot etc.
It's a great time of year to search for passage migrants at Flamborough Head and Spurn, although photographic opportunities may not be guaranteed. The RSPB also do cruises from Bridlington searching for skuas and shearwaters during that time, but these need to be booked in advance.