Reading the initial thread post I was thinking that achievements badges would be cool. There's always milestone achievements like 50, 100 NES games and so on. I was thinking more outside of the box.
Dream Weaver: Entry you created is in 10 Wish Lists.
Phone Home: Remove Atari 2600 game ET from your collection.
Wish-a-Pawn-a-Star: Someone contacts you about an item in your Sell list that is in their Wish list.
Got to catch 'em all: Pokémon Red, Blue and Yellow are in your collection, complete in box.
Domo Arigato: Added a Japanese console to collection.
If You Build It: Entry you created is in 20 collections.
Revision-a-tron: Submitted an Edit to entry created within the past 4 hours.
Day One: Add item to collection on the same day of its release.