It seems to me that this proc is pretty singular -- after a little bit of searching, I can't find any other weapons that have anything like it. If you can, let us know in the comments below.

Name: Rod of the Sun King (Wowhead, Thottbot, WowDB)
Type: Epic One-hand Mace
Damage/Speed: 189-352 / 2.70 (100.2 DPS)
Abilities:

• Increases attack power by 52.
• Chance on hit: gain 10 energy or 5 rage. This is the proc (short for procedure, from the programming world, though it's come to mean a number of other things) that really makes this mace stand out as a choice pic for Rogues or DPS Warriors -- the proc rate seems to be around 3 procs per minute, which is a substantial amount of energy and rage coming back to the user.
• Unfortunately, it also seems there's a short cooldown on the proc, which means you can't have a bunch of procs in a row, and get a bunch of free energy or rage back to back. Still, this weapon provides a pretty steady source of extra Warrior/Rogue fuel, and it's exceptional for that reason.

How to Get It: Drops from Kael'thas -- the Tempest Keep version, not the Magisters' Terrace one. The drop rate is somewhere between 15 and 20%, but the proc on this weapon makes it pretty specific -- only Warriors or Rogues would ever be able to use it to its fullest, and even then, it's definitely not a tanking weapon. Rogues may be tempted to switch to a Mace spec just to use this, but Warriors would only need it for a DPS set.

Druids, unfortunately for them, have no use for this weapon, even the bear kinds. Since the proc requires a "chance on hit," and bear Droods don't actually hit anything with their weapon (just their paws), it'll never proc for them. Blizzard might have been a little more giving on that one, but as it is, this weapon doesn't help bears at all.

Getting Rid of It: Sells to vendors for 14g 59s 25c, disenchants into a Void Crystal. There will be other, better weapons you find on your way up the raiding ladder (and while the DPS on this is nice, the high-end Arena gear beats it), but the proc on this weapon is almost enough to keep it anyway.

Blades of Light! In one of the best-loved (and most traveled) instances in the game, you'll find this axe with what might be the most fun proc in the game.

Name: "The" Ravager (it's actually just Ravager, but this weapon is so cool it deserves to be singular)
Type: Rare Two-hand Axe
Damage / Speed: 104-157 / 3.50 (37.3)
Abilities:

• For the down and dirty on today's Phat Loot, we're going straight to Isobelle over at Not Addicted, who says, "Why do I have such a stiffy for this Radiant Shard in Waiting? Take a look at that proc!
  
  Chance on hit: You attack all nearby enemies for 9 sec causing weapon damage plus an additional 5 every 3 sec.
  
  Are you kidding me? ALL NEARBY ENEMIES? Whirlwind hits only four additional enemies, has a ten second cooldown, only works in berserker stance, and has a cost of what some might call "much rage". This thing costs zero rage, works in any stance, and will hit as many enemies as you can get into melee range before it procs." Yeah. She loves it. And we do too.
• The only problem? Whenever it procs, you stand there spinning for the whole nine seconds, whether there are enemies around when you're done or not. We're talking endless entertainment here. Isobelle: "It procs All Day Long. It procs procs, which then proc a proc. We've seen it go 4 times in a row, which can be a good thing, or a bad thing. That's like 20 seconds of whirlwind vortex love (when it re-procs, the 9 second timer resets, so you don't get a full 4x9 out of it), but sometimes you want to turn it off. You can't."
• And Isobelle didn't mention it, but we will: the thing looks darn cool, too. As part of Herod's Scarlet set, it goes especially well with his helm and half-shoulder, too.

How to Get It: No quests, just lots of elite, instanced killing. The Ravager drops from Herod, the last boss in the Armory part of the Scarlet Monastery (to get inside there, you'll need the key from the end of the Library wing, but everyone runs SM all the time, so it's likely someone you know will be able to get you in with or without the key). The drop rate stands at about 12%, which isn't bad, but the fact is that this axe is great for anyone who can use a two-hander, so if you have any other heavy melee classes in your group, it's likely you'll have to win a roll for it.

Oh, and if you haven't noticed yet, Herod yells "Blades of Light!" a lot. Isobelle recommends setting up a macro to /yell that phrase whenever this procs, and we concur.

Getting Rid of It: BOP, Disenchants into a Small Radiant Shard, sells to vendor for 1g 89s 23c.