Quel'delar in Thirteen Easy Steps

Well, really fourteen steps. But I didn't want to discourage you. Patch 3.3 will contain, in addition to a legendary 2H DPS axe that will send your hard-mode 25 raiders into raptures, a Very nice DPS weapon for everybody else. Weighing in at iLevel 251, the reward for this quest chain beats out all the gear you can get in 5-man content anywhere, most of the gear you can get in earlier tiers (hard-mode 25-man ToC gives iLevel 258 rewards), and is on par with drops from the 10-man version of Icecrown Citadel. It's a really good weapon to work for, especially since it can be gotten by new raiders. If you're gearing up your DPSer, it's worth picking up.

Who can use Quel'delar? Any class, really. It is a DPS weapon, although tanking Death Knights and healers can probably use it as well, as the stats on it align pretty well with what death knights and healers want as well (except for a lack of MP5 on the caster weapon). There are rewards at the end of the chain that look like this:

Quel'Delar, Might of the Faithful - 2H strength sword. Warriors, Death Knights, Paladins, etc.
Quel'Delar, Ferocity of the Scorned - 2H agi sword. Who uses these? Maybe a hunter?
Quel'Delar, Cunning of the Shadows - 1H sword, mostly for Rogues, although hunters might use one if they've got a good OH.
Quel'Delar, Lens of the Mind - Caster sword (warlocks, mages)
Cudgel of Furious Justice - 1H DPS mace. Probably mostly for enhance shaman.
Hammer of Purified Flame - Mace caster (priest, shaman, paladin) reward.
Lightborn Spire - The feral druid reward.

How do you get Quel'delar? First, you have to get a battered hilt. That drops in the new 5-man instances in 3.3. It drops from trash mobs, and we don't really know the drop rate yet, but it is not BoP at this point. Meaning, worst-case you can buy one (or send it to a friend as a gift). Once you have the hilt, it's just a matter of running some errands, some of which require you to beat the new 5-man content (like you weren't going to do that anyway). The whole chain is as follows:

1. The Battered Hilt - Just turn in the hilt.
   
2. What The Dragons Know Go talk to some guy.
   
3. The Sunreaver Plan Kill some dude in the underbelly. Loot.
   
4. A Suitable Disguise Go talk to some other guy.
   
5. A Meeting With The Magister You guessed it - talk to some other guy.
   
6. Return To Caladis Brightspear Yet again. Talk to some guy.
   
7. Reforging The Sword Here's where it gets interesting. You have to go into the Pit of Saron, get 5 groundspawn drops (which also drop from trash), and then get a quest item off of a boss. It seems like you can get the infused saronite solo if you want - just use the normal mode instance, get the two near the door that aren't guarded, reset and repeat. You still need help killing the boss, though. Note that this doesn't require a heroic run.
   
8. Tempering The Blade Run the forge of souls, and there's a crucible to temper the blade after the last boss. Again - not heroic.
   
9. The Halls Of Reflection Go to the Halls of Reflection with four friends, fight the Spirit of your Sword (of course, ignoring Uther Lightbringer's advice to go home and have a sandwich instead of proceeding).
   
10. Journey To The Sunwell Go talk to some dude. In this case, the dude outside the Sunwell, so he lets you in.
    
11. Thalorien Dawnseeker This is the dude at the Sunwell. Talk to him.
    
12. The Purification of Quel'Delar Stick your sword in the Sunwell. Party down.
    
13. A Victory For The Silver Covenant Pick your prize! There's actually two versions of this quest, I don't know how people end up getting the Sword version or the Mace version, I imagine that mace-users (priests, shaman, druid) get the mace-quest.

And there we have it. It's a lot of walking and talking, but there's some dungeoneering in there. Still, with four solid friends, you should be able to do this in an evening, once you get your hilt. It's currently unclear whether you'll need to run those instances multiple times if there are several people in the party on the same step, or if you can double-dip. Time will tell.