LFDAutoJoin 

LFDAutoJoin automatically joins ready LFDs. It's very lightweight and has little customization.

LFDAutoJoin has a polite AFK behavior: if you are AFK you will still auto-join the instance, but after zoning you will print a friendly BRT (be-right-there) message to /party (or /say if the party wasn't initialized yet--e.g. latency). These AFK messages are configurable in the LUA file.

LFDAutoJoin will also play a custom sound when a LFD is ready, one more noticeable (possibly annoying) than the default. This sound is optional/configurable. You can also choose to only play the sound when AFK (default).

The sound and its credits:
http://www.freesound.org/samplesViewSingle.php?id=18075

Toggle enable/disable of LFDAutoJoin (saved per account):
/lfdauto

Please use LFDAutoJoin with respect to others. Heroics are repetitive, people are impatient; don't let them wait for more than a minute.

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CONFIGURATION
----------------

Refer to LFDAutoJoin.lua to make changes.

Defaults:

local showAfkMessage = true
local playSound = 2 -- VALUES: false, 1 = Yes, 2 = Only When AFK

local afkMessages = {
    "I'll be ready soon, just need a sec.",
    "Be right there guys, need a sec.",
    "Hey all, I'll be ready in just a bit.",
    "Hi, need a sec to be ready.",
    "Hey, I just need a sec to begin.",
    "Hello, I'll be ready in a sec."
}

local soundFile = 'Interface\\AddOns\\LFDAutoJoin\\ready.mp3'