To alleviate the strain that LFG and LFM requests have been putting on guild chat, and to avoid the need to monitor a separate LFG channel, the Alea Iacta Est Skunkworks Division has put together a modified version of an add-on that was made obsolete by the introduction of Blizzard's LFG tool. The add-on is called aieCallToArms, and is a modifed version of CallToArms.

What does it do? It allows you to advertise slots for instance groups and announce your own looking for group status. It uses its own data channel for exchanging information, but also sends human-readable messages to the impromptu aieLFG channel and can recognize requests that are said in that channel and track them.

Our own Thelial has put together a user's guide for aieCallToArms that should get you working quickly.