The Dragon Below

The Hall of the Revered lies beneath the Spires of the Forge.
Enter the door above the tangled valley.
Look neither left nor right. The riches there are not for you.
Hold to the path that leads to the Hall and find what waits in the shade of the Grieving Tree.

A trilogy of Eberron novels by Don Bassingthwaite detailing the adventures of a shifter named Geth, a wizard named Singe, and a kalashtar named Dandra who has a dark secret. The three are joined by many more on their quest to stop the Servant of Madness, the priest of the Dragon Below, Dah'mir, and the barbarian tribe known as the Bonetree that he controls. Notable among novels based on D&D campaign settings in that it doesn't suck. The three books in the series are:

The Binding Stone
The Grieving Tree
The Killing Song

Also has a sequel trilogy written by the same author and using some of the same characters, The Legacy of Dhakaan.

Needs More Love

Tropes used in The Dragon Below include:

Action Girl: Dandra
Big Bad: The Master of Silence
Badass: Most of the main characters, but Geth and Ashi spring to mind.
Defector From Decadence: Ashi, from the Bonetree.
Determinator: Dandra. Literally. She is determination.
Deus Ex Machina: A very well done type 4 when Ashi manifests the Siberys Mark of Sentinel, something that has been hinted at for two and a half books.
The Dragon: Dah'mir to the Master of Silence, Medala to Dah'mir. Until Medala tries to take over Xoriat.
Eldritch Abomination: The daelkyr.
Evil Sorcerer: Dah'mir. Possibly subverted, given that as a dragon his abilities are innate, rather than learned.
Magic Knight: Singe is very good at combining magic with swordsmanship; in a variation, Dandra is a psionic warrior, rather than a magical one.
Magic Music: Ekhaas and the other duur'kaala.
Playing with Fire: Singe, of course, but also Dandra to a lesser extent.
Power Born of Madness: Literally, in the case of the stronger servants of the daelkyr.
Proud Warrior Race Girl: Ashi.
The Reveal: Dah'mir is a fucking dragon??
- and also that Dandra isn't really a kalashtar, but the psicrystal spirit created by the kalashtar Tetkashtai, trapped in her body.
Sealed Evil in a Can: The Master of Silence was sealed away again at the end of the trilogy.
Title Drop: Kinda sorta. The phrase "the binding stone" isn't used until the second book, and "the grieving tree" is mentioned in the little poem at the beginning of the same book, seen above.
Unfortunate Names: Singe seems to think his real name (Etan Beyard) is a curse--partly because he doesn't like it, and partly because he hates his family. Besides, if you could get away with being called Singe, wouldn't you use it? Also leads to Do Not Call Me "Paul".