I'll start off by saying this isn't a guide, just some really cool ulduar lore; however, I thought this was something worth sharing. The main reason I want to share this is because a lot of people won't see this in WoW, at least not for quite a while, unless you are in a very hardcore raiding guild.
{{SPOILERS AHEAD}}
Anyways, the main reason most people will not experience this content is because Algalon is the only "optional" boss in ulduar and he only has a hard mode (hard mode is the equivalent of sartharion with three drakes up). In addition to this, the only way to unlock his room will be to complete the four watcher bosses (freya, hodir, thorim, mimiron) on hard mode and obtain certain items off them. Within blizzard Algalon is known as "Algalon the Raid Killer", he'll most likely be one of the hardest encounters to date in the game, if not the hardest.
A little bit of backround information before I give out the youtube link. I don't take credit for datamining this, a guildie of mine found it and showed it to me. Huge props to dataminers who get this stuff outta the PTRs. Anyways it's a very, very cool video and I hope you guys enjoy it.
[ame=http://www.youtube.com/watch?v=r2MwblTnb-g]YouTube - Algalon the Observer Sounds[/ame]