I have to say the Clockwork rifle, it really changed my first time into hardmode for the better. And was quite useful until I learned about the Megashark, so I still very much enjoy the weapon as it is. And I'm hoping that when I get to hardmode again that I get because it is so useful for early hardmode.
The inferno fork. I decided to try and get a shadow beam staff and instead I got this, and I couldn't be happier! When I got it it already was reforged to mythical, so it did like 100 something damage. Mythical inferno fork + specter hood = fastest healing EVA
The Bees Knees is probably it for me: It takes down the wall of flesh, and keeps me alive through early hardmode until I can get better weapons, generally the Daedalus stormbow, followed by light discs/yelets. I once had to take down an expert mode pirate invasion with nothing but the bees knees and, while it took FREAKING EVER it did the job. Turns out if you get enough bees together, you can take down flying pirate ships given enough time.
during my PC playthrough, i found the minishark and megashark super helpful in taking down bosses because 1: it has a very fast fire rate and decent damage. 2: i don't have to get right up in the bosses face and potentially risk getting eaten and 3: it has a chance not to consume ammo [off you go ammo reserve potion!]