Minecraft Wiki
The Minecraft Wiki is the ultimate resource for any Minecraft player. It has information about everything in Minecraft including blocks, items, trivia, and glitches. When in doubt about any Minecraft fact, check the wiki!
Bukkit
Bukkit has the largest collection of plugins on the entire Internet. If you're a server owner, Bukkit is the ultimate resource for plugin information. Many servers use Bukkit's API, CraftBukkit, to run the various plugins that make up their servers.
The Minecraft Forum
Have a question the Minecraft wiki can't answer? Want to chat with other Minecraft players? Want to find a server? The Minecraft Forum is a great place to chat with like-minded Minecraft players and discover interesting facts about Minecraft.