There aren't a whole lot of secrets in Dragon Quest 6- but here they are.
The Orihalcon Fang
First, you'll need to have beaten the game and reached Death Cod. In Death Cod, you'll find a monsters up in the second floor of the pub. Talk to the demon.
The demon will give you those instructions. Unless you've talked to him, you can't get the fang so don't try getting it before you come here- you're wasting your time. Leave Deathcod and head to Calcado. Follow the instructions, and you'll find the Orihalcon Fang- the 3rd most powerful weapon behind the Gringham Whip and the upgraded Sword of Ramias.
The Meteorite Armband
The Meteorite Armband is missed by almost everyone. To get it, head to Dream World Amoru- I'm not sure at what point in time you can do this to be exact. Head to the church.
You'll see these two children playing in the corner. The text isn't translated in the patch so I don't know what they're saying exactly ^_^;;. After they're done, Iria's name pops up- the kids were Gina and Iria.
Now go searching where they were- another message pops up. You're done here- return to the Real World Amoru now. Search where they were burying the item in the Dream World, and you'll find the Meteorite Armband.
The Armband will multiply your speed by 2- a very nice accessory.