Got a few things from the final boss, martian invasion, expert mode bosses, and the pillars. Don't have pics, but I ran the final boss around 5 times to get both the Solar Flare Armor and Nebula Armor for a friend.
Solar, Nebula, Stardust, and Vortex Fragments: Used to craft the endgame weapons and armor. Dropped from their respective pillars.
Luminite and Luminite Bars: Drops from final boss, used to craft the four endgame armors and wings.
Solar Eruption: Chain-knife style flail, pierces through all terrain and enemies, and causes explosions upon hitting an enemy. Crafted using Solar Fragments.
Daybreak: Throwing spear which never runs out, does large amounts of damage, does damage as the spears are stuck in. Crafted using Solar Fragments.
Stardust Dragon Staff: Summons a wyvern like dragon. Multiple casts will add more segments onto it. Really good, even for non-summoners. Crafted using Stardust Fragments.
Stardust Cell Staff: Summons a cell to fight for you. Multiple uses adds more cells. Honestly, i'm confused on how this exactly works. It does damage, and leaves spheres on whatever's still alive. Crafted using Stardust Fragments.
Portal Gun: It's literally the Portal Gun from Portal. Sprite and everything. Drops from final boss.
Space Dolphin Machine Gun: Seen through hacks, but now obtainable. Basically a better Megashark. Drops from final boss.
The Terrarian: Fancy YoYo, sends out bolts of energy around it (which home when near enemies) wherever you aim, does lots of damage. Drops from final boss.
Zealous Lunar Flare: Upgraded Blizzard Staff with somewhat explosive properties. Drops from final boss, very good against the horde events.
Solar Flare Armor: Has aggro, 33% more melee damage, and a "Solar Shield" as a set bonus. Basically, it reduces damage done to you by 30%, and allows you to dash into enemies. Also causes pushback to enemies hit. Very good armor, far more tanky than the Beetle, with more damage. Crafted using Solar Fragments and Luminite Bars. (you'll probably need two runs to get enough Luminite.)
Nebula Armor: Mage armor, not sure of the stats, but the set bonus is AMAZING. Essentially, causing damage has a chance to spawn buffs (30% more damage, really fast health and mana regen, etc.) Allies or you can pick them up, and the chance for the buffs to drop is really high with some of the magic weapons.
Brain Scrambler: Summons a rideable alien scorpion like mount. Quite fast, fires lasers at enemies. Drops from ssomething in the Martian Invasion.
Shrimpy Truffle: Summons a mini-Fishron mount. Can fly forever. Moves faster the more you are damaged. Dropped by expert mode Fishron.
Mechanical Cart: A super minecart which moves really fast and fires lasers. Parts are dropped from the Hardmodes mechanical trio. (Yeah, eahc of them has a single part for it)
There's more stuff, but i'm still looking into finding it.