I think my friend and I are really scraping the bottom of the barrel for things to do now.
We've defeated Plantera a couple of times (It's really easy when it chases you around the outside of the Jungle Dungeon), have defeated the Golem a stupid number of times to get everything bar the Stynger and have mined enough Chlorophyte to get ourselves the top-tier armours (My friend is already in Beetle armour).
The only thing left for us is to do the Pumpkin Moon/Frost Moon events, which we're soon to do.
And other than that it's hope to get a keymold so we can go and get something of use from the Dungeon, which happens to be ridiculously tiny on our Large World. The version on my Medium World was bigger, and having spent the same amount of tgime in it I've not uncovered every route, which we've done in our Large World.
I do love Terraria, and it's a lot of fun, but we definitely need a goal to keep us interested.