Mercedes Lackey

Fairy Tale

1. Firebird (read pre-blog)
2. The Black Swan (read pre-blog)

Bard's Tale

1. Castle of Deception (read pre-blog)
2. Fortress of Frost and Fire (read pre-blog)
3. Prison of Souls (read pre-blog)
4. The Chaos Gate by Josepha Sherman
5. Escape From Roksamur by Mark Shepherd
by Holly Lisle:
Thunder of the Captains (1996)
Wrath of the Princes (1997)
Curse of the Black Huron (1998

Elemental Masters

1. The Fire Rose
2. The Serpent's Shadow (read pre-blog)
3. The Gates of Sleep (read pre-blog)
4. Phoenix and Ashes (read pre-blog)
5. The Wizard of London
6. Reserved for the Cat
7. Unnatural Issue
8. Home From the Sea (tbp June, 2012)

Valdemar

After a lot of googling, everything I've read says it's best to read the books in the order they were published. So I've come up with this list that is chronological by publishing date but keeps trilogies together. If you are a fan and think I've made a grave error in order here somewhere please let me know.

Arrows of the Queen, 1987
Arrow's Flight, 1987
Arrow's Fall, 1988

Magic's Pawn, 1989
Magic's Promise, 1989
Magic's Price, 1990

The Oathbound 1989
Oathbreakers 1989
Oathblood 1989

By the Sword 1991

Winds of Fate, 1991
Winds of Change, 1992
Winds of Fury, 1993

Storm Warning, 1994
Storm Rising, 1995
Storm Breaking, 1996

The Black Gryphon 1994
The White Gryphon 1995
The Silver Gryphon 1996

Sword of Ice And Other Tales of Valdemar, 1997

Owlflight, 1997
Owlsight, 1998
Owlknight, 1999

Brightly Burning 2000

Exile's Honor, 2002
Exile's Valor, 2003
Take a Thief, 2004

Sun in Glory And Other Tales of Valdemar 2003
Crossroads And Other Tales of Valdemar, 2005

Moving Targets and Other Tales of Valdemar, 2008

Foundation (2008)
Intrigues (2010)
Changes (2011)

Changing the World: All New Tales of Valdemar (edited by mercedes Lackey) (2009)
Finding the Way and other tales of Valdemar (2010)