Am pretty sure most of you know and been to Wikipedia. But... Have you been to Halopedia? And you can find info about:

• [+] Halo 3 Achievements
• [+] Halo 3 Beta
• [+] Halo 3 Campaign Missions
• [+] Halo 3 Multiplayer Medals
• [+] Halo 3 Ranks

Halopedia, the Halo Wikia, the definitive source for Halo information. Even more they have pages for other games such as:

Hopefully this site will be of help for all of us when having doubts or questions about a game.