My list was also boosted by recent visits to two cracking nature reserves: Leighton Moss and Potteric Carr.
Leighton Moss must be the easiest RSPB reserve to reach by public transport. The entrance is just a short walk from Silverdale railway station and there's now a bus (dubbed the Bittern Bus, no less) which links the reserve with nearby villages.
Although it's closer to home and in an urban setting, Potteric Carr is a little trickier to access by public transport. The no. 72 bus from Doncaster Interchange stops nearby (outside B&Q on Woodfield Way) but you have to negotiate your way across a couple of busy roads to reach the reserve. The no. 75 bus to the Lakeside Shopping Centre is more frequent than the no. 72. From Lakeside, it's a less than pleasant walk of about 500m along White Rose Way to Potteric Carr - it's shame the council didn't include pedestrian access when they built this road!