Yes I'm going to talk about a tower-cap bed. No, my most valuable was a 90k gold shortsword covered in rough gems and human bone. Yes the bed was better.
Context: This was my first HFS game (that I know of). I accidentally landed on a chasm (as well as a ton of native platinum and other fun things, which I expect is the norm on dangerous terrain). My wagon was parked RIGHT NEXT TO IT. It was also some six squares or so away from my fortress entrance, AND three z-levels up. I was on a no-anvil, no-axe, lots of wood build. This was bad.
It was in late fall, just before the first caravan when my carpenter left his post in the kitchen in a mood. He ran /straight/ for the chasm, which had already cost me an herbalist and all of my cats. He grabs three logs out of the wagon and creates a 3,600 bed with an image of the current King. I think he wanted to be ready when the King showed up to personally over see all the platinum I was going to extract.
This artifact was PERFECT in every way:
1) It gave him Legendary carpentry status which meant he was now ten times faster. He was fast enough, in fact, that if he was ever interrupted at the carpentry workshop I built at the wagon (before I realized it was next to the chasm), he could run faster than anything chasing him.
2) It gave him Legendary carpentry status, which meant he had the shortest possible loiter time at the workshop, also helping increase his lifespan.
3) I was now able to crank out all the bins, barrels, and beds I had the wood for (and then dissassemble the workshop and move it inside) in a single month and without endangering anyone else.
4) It was cheap, so I didn't have a tsunami of immigrants kill my entire food stock and cause a tantrum spiral (that happened two seasons later when I had back-to-back 40k-ish artifacts and the lack of cats meant a huge vermin problem).
5) I now had a bed with the King's name on it.
Too bad #4's caveat happened.