Most games give out NP as opposed to items. The only games I can think of that you get items from are Gormball (if you win the game - the items aren't usually very good though), and Neoquest/Neoquest II (where the prizes are only really worthwhile when you play in insane mode). Otherwise, you could try the quests - Snow Faerie seems the most likely to give out decent items, but the Esophagor and Mystery Island Kitchen quests can give out some nice ones too. You have to weigh up the cost of doing the quest though as you can often end up making a loss.
You could try the deserted Fairground games. I'll usually play coconut shy, I've won a few hundred thousand NPs from there along with coconuts worth quite a bit. Whenever a new game gets released, you'll get a chance to beat AAA and get a prize as well, but those aren't worth as much.
oh... but when i run ssers i sometimes have bottled faeries and other items in my inventory. is this bc of the world challenge thing? (idk what that is exactly.) but i might be wrong, bc i haven't run an sser in a while.
the best i'd say, has to be key quest... i really like let it slid, wheelers, and faerie cloud racers(both) also. It depends on you, but if your looking for SERIOUSLY BIG BIG BIG NP, i say Key quest.