I apologies first to all who made a thread of similarity to this already as I do remember at least 2 threads of a similar nature but I felt that by now they are long dead and my idea would be a bit too far for it to function as a post suggestion.

I personally love the achivments in this game and had a fun time unlocking most of them. The few I do not have are on my list none the less.
I feel that when ever you get one of the ending achievements like mad hatter and Dauntless Diver you should recive some form of a bound costume as a reward. I don't have a complete idea of how it should look but none the less the shield, armor, and helm should all be either prismatic or a good neutral color to work with most personal colors.
I did consider that it should be a well draped and armor with purple to go with the purple spiral but I dunno :l

What about the weapon achievements? and heck, even the shield one?"
I think for these the player should be rewarded with a bound recipe that provides them with a "side grade" to the valiance, Nitronome,Levianthan blade, and maybe? the Omega shell. I know that the Agies would make more seance but until we get costume shields I feel the omega shell would work best as it can be used rather easily any were as it is simply a purely strong shield.
For the look of the swords I feel they should be either a white/prismatic combo or a similar look to the armor this way it can work as a full set.
The crafting for these "side grades" should only cost materials, and not much at that. The end weapon/shield will be untradable and undropable just like the rocket hammer and DR.

Any thoughts? feel free to say what you think.

LATE EDIT: sorry.
I think the armor and helm achievements should reward costume pieces to be paired with the sword, the Dauntless Diver and the "Cradle and All" achievements should provide bomber style costume to be paired with the gun and the "Full loaded" and the "Master Miner" achievements provide a gunslinger style costume for the gun.
I can't come up with a shield bearer set and what achievements should be hooked up with it.