The latest WoW patch notes can always be found at http://www.worldofwarcraft.com/patchnotes/
Current patch: World of Warcraft Client Patch 2.4.2 (2008-05-13)

Public Test Realm patch notes can always be found at http://www.worldofwarcraft.com/patchnotes/test-realm-patchnotes.html
Current patch: World of Warcraft PTR Patch 2.4.3

Older WoW Patch:

Patch 2.3.0 | Patch 2.2.0 | Patch 2.1.3 | Patch 2.0.12 | Patch 1.12 | Patch 1.11 | Patch 1.10 | Patch 1.09 | Patch 1.08 | Patch 1.07 | Patch 1.06 | Patch 1.05 | Patch 1.04 | Patch 1.03 | Patch 1.02