The bar at the BlueZoo is the most "upscale" (and beautiful)
Maybe not exactly upscale but a nice is atmosphere is Belle Vue Lounge at the boardwalk villa's. It is kind of hidden
For the monorail:
Grand Floridian has a several:
Mizner's Lounge (this is by itself)
There is a bar at the Citrico's restaurant that looks nice and so does Narcoosie's
I am a big fan of the Crew's Cup at the YC. Belle Vue lounge is also nice if you can get one of the outside tables, allowing you a view of the Boardwalk.
I think it has rum, lemon juice, and maybe an orange liqueur w a cinnamon rim. You could google it. It's so delicious. I've made them at home but they aren't as good.