Expansions

Perfect World International was first released as an Open Beta on 9/2/2008 (see this thread). Since the game was not reset once the Open Beta ended, this is considered the official release date of the game. Since then there have been a couple of major expansions to the game, which are listed below.

Lost Empires

Released: 12/2/2008
Links: patch notes / expansion page

Added many new high-level skills for each of the original six classes (archer, barbarian, blademaster, cleric, venomancer, and wizard).
Added the Chrono Quests.

Age of Spirits

Released: 5/13/2009
Links: patch notes

Added genies. (Many changes were later made to genies in the 9/15/2009 patch.)
Added auto-pathing to quest locations and the "Find Quest" option in the Quests window to find new quests.

Rising Tide

Released: 12/16/2009
Links: patch notes

Added Tideborn lands (three new zones) and assassin and psychic classes.
Added the Raging Tide PvE server.
Added the Palace of Nirvana.
Added a gear upgrade system for high level gear.
Added Public Quests.
Added Marriage Quests.
Added Tidal Protection Charm Quests.
Added Account Stash.
Added TAB targeting.
Added custom key settings.

Genesis

Released: 3/2/2011 (soon to be released)
Links: expansion page

Added Earthguard lands (four new zones) and mystic and seeker classes.
Added faction bases.
Added Runecrafting skill.