I occasionally browse the official Warner Bros store.
US:
https://www.wbshop.com/UK:
https://shop.warnerbros.co.uk/They sell various merch, blu rays/UHD 4K blu rays, steelbooks, collector's items, merch, clothing, video games and what have you - with new items showing up and sales happening from time to time on things.
They have a lot of things related to DC super heroes and HBO shows but other franchises and movies too.
Do you know of any other cool places to dump spare cash?