Does anyone keep a list of save file locations for GoG games?
A lot are in the usual places (AppData, the installation folder) but even then the actual files or locations aren't entirely obvious sometimes.

I'm just looking to back some saves up so I can uninstall some games that I've not been playing and make space for some new ones.

I can't imagine there's any kind of back up program that doesn't involve a client that would find and back up the saves automatically, but if such a thing exists that would do..

Thanks!

I would recommend looking up the game on PC Gaming Wiki, I use that site just for that information:
http://pcgamingwiki.com/wiki/Home
For example:
[url=http://pcgamingwiki.com/wiki/Shantae:_Risky's_Revenge_-_Director's_Cut#Save_game_data_location]http://pcgamingwiki.com/wiki/Shantae:_Risky's_Revenge_-_Director's_Cut#Save_game_data_location[/url]
In this case gives the location for the Steam version, but it gives you an idea, for example, of the sub-folder name you may be looking for.
Another example:
[url=http://pcgamingwiki.com/wiki/Dust:_An_Elysian_Tail#Configuration_file_and_save_game_data_location]http://pcgamingwiki.com/wiki/Dust:_An_Elysian_Tail#Configuration_file_and_save_game_data_location[/url]

Thanks, that's just the kind of thing I was looking for :)

No problem! :)