Blizzard Entertainment - StarCraft: Brood War
Official site with information on new additions to the game.
GameSpot's Starcraft Expansion Set: Brood War
Features an introduction, race overview, campaigns, and cheat codes.
MacNN - StarCraft: Brood War Expansion Pack
Features a description of the new additions and changes.
StarCraft Brood War Second Expansion
Petition and guestbook for ideas on an expansion set.