Drops from Supremus (http://www.wowhead.com/?npc=22898) in Black Temple.
Great bracers. Netherstrike Bracers are good too, but they are better at the longevity aspect. I would recommend getting those if you can and slapping 6 mana per 5 on them, then get these (if you can) and put spell damage on them.
Switch out as the encounter demands.
Graphically matches Skyshatter Armor (Shaman Tier 6).
Of course you could also ignore the socket bonus and dump a runed crimson spinel in it, but purely PvE wise the Bands of the Coming storm are light favorite due to the mana effective.
While these are great, the only concern is that there's an easy-to-attain 35-badge leather wrist called Armwraps of the Kaldorei Protector that either competes with it, or if gemmed certain ways, is actually better on spell crit and spell damage stats.
For a tier 6 Black Temple Supremus rare drop... that's pretty embarrassing. Either the Armwraps need a nerf or these need a buff.
The only edge you get out of these is bigger int, stam, and armor, so they're very slightly better for simple survival in tier 6 content.
I actually have the Vindicator's Mail Bracers and I have them socketed with the +12 Spell Crit gem since I'm a JC, and I prefer them.
These use the Black variant of the "Raid Shaman F" artwork (the Blue version of this art was used for the Shaman Skyshatter (Tier 6) set, except for the bracers, belt and boots).