Official errata for the Planar Handbook can be found in the following archive on the Wizards of the Coast website:
http://archive.wizards.com/default.asp?x=dnd/er/20040125a
Additional, unofficial errata (by Tim Emrick) follows.
p. 15, Spiker Racial Traits: See Official Errata.
p. 46, Aton Hollysprig, the Defiant: Aton is human, so should have one additional feat. Under Spells, move shield other to 2nd-level spells, and add two more 1st-level and one more 3rd-level spells. He has been given no domains, but his spells prepared numbers include domain spells. Based on his spell list, he should have the Protection domain; mark sanctuary, shield other, oneprotection from energy, and spell immunity as domain spells, and give him the protective ward granted power. Choose one other domain compatible with his alignment, and give him that granted power.
pp. 51-52, Andrea Lethyr the Fatemaker: Add "confidence of the fated" to SA. Andrea is only a 3rd-level fatemaker, so delete the Aura of Confidence paragraph.
pp. 57-58, Felice the Ardent Dilletante: Her Exotic Weapon Proficiency must be applied to one specific weapon, but she carries no exotic weapons to make the choice obvious. As a bard, she is proficient with the whip, so does not need the feat to qualify for her prestige class; replace it with a more useful feat.
p. 74, Planar Sailer: The details of the special plane shift power (such as how often it may be used) are not given.
p. 78, Slimy Armor: See Offficial Errata.
p. 81, Rod of Celestial Might: See Official Errata.
p. 81, Staff of Abyssal Iron: See Official Errata.
p. 89, 1st-level Cleric Spells: See Official Errata.
p. 118, Elysian Thrush: The thrush is a magical beast, so Base Attack/Grapple should be "+1/-12". The attack modifier for its claws is correct.
pp. 124-125, Gaspar: As a 14 HD monster, a gaspar should have 5 feats but has only been given two. Add three more. (My suggestions would be Dodge, Endurance, and Run.)
pp. 127-128, Lesser Nightmare: See Official Errata.
pp. 128-129, Pack Fiend: Under Feats, the "B" after "Track" should be superscript.
Tim's Appendices
Planar Touchstones
The following table sorts the touchstone sites by plane. Planes are listed in the same order they appear in the Planar Encounters appendix.