In no particular order
@cnrgtl’s Master’s Project, particularly the idea of vaults, that we now see as Pots, but there is so much good stuff in there.
Monzo’s new look - Although I’m not a massive fan of the current app design, this thread and @bruno gave a pure masterclass in community engagement.
@Revels fantastic dashboard and @MalaiseForever spotting this in the guide which has spawned an in community joke.
The launch of Summary - It didn’t, and still doesn’t suit everyone but I remember really looking forward to this feature coming to the app. It was a big new feature that was open to all, even if it didn’t suit them. While I’ve used it less over the years I still value the Red/Amber/Green bar with the little ticker on the home screen. Perhaps that’s more of a monzo moment than a community one, but it did create a lot of buzz in the community.
The recent buzz in the community is also right up there for me, particularly with the new neon cards for the community thread. Team 
