Prat - a chat enhancement addon made up of modules which can be enabled that provide additional functionality. You can format how players names look in chat including their class color and level. There is an alt module that scans your guild log to find players alts, it then adds their main name in chat in parens after their current character name. It provides the ability to bind keys to chat channels, I hit G to type in guild chat.
Anti_Spam - Addon with a simple UI to filter your chat by adding keywords or character name.
Cleaner Loot Messages - Reduce loot messages to a minimum for clearer information.
devnull - When you enter a capital city it will ignore people who /yell. It will ignore spammy NPCs (ie. Ironforge bread vendor, Topper McNab in Stormwind etc). It will ignore duel spam (A has defeated B in a duel). It will ignore emotes except those directed at yourself. It will ignore drunk spam (X looks tipsy). It will ignore tradeskill spam.