Thanks for the ideas! So far, I'm torn between the Talisman of Colorless Fire and the Crystal of the Ebon Flame. I'll take any other ideas anybody can pitch out, too.
I ran a really long 2nd Edition campaign that involved the players trying to find all the Teeth of Dahlver-Nal. It was some of the most fun I've ever had playing D&D.
Some other good ones from the 1e DMG (though nothing to do with fire) are the Iron Flask of Tuerny the Merciless, the Jacinth of Inestimable Beauty, the Ring of Gaxx and the Teeth of Dahlver-Nar.
I ran a really long 2nd Edition campaign that involved the players trying to find all the Teeth of Dahlver-Nal. It was some of the most fun I've ever had playing D&D.