I wear a full set of molten armor.  

I use Muramasa, Blue Moon and a Pheonix Blaster as weapons.  

I defeated the Eye of Cthulhu, the Eater of World and Skeletron.  

I killed a goblin army without ever being in any real danger.  

I explored the Dungeon, the Underground Jungle and the Underworld.

What is there left to do? 

* What is there left to kill that might still provide a challenge?
* What places are there left to explore that still contain some secrets?
* What ludicrous buildings or contraptions are still to be to build?