Zekrom, a new member of the base 150 Attack group. That means it ties attack with Groudon, Rayquaza, and Normal Forme Deoxys. Like Groudon, though, it's a tish on the slow side, packing only base 90 speed. On the onther hand though, Zekrom has admirable bulk, 100/120/100 in its defenses is quite nice for an attacking Pokemon. Its stat spread is mirrored to Reshiram, so Zekrom had higher Attack and Defense whist Reshiram has higher Sp. Attack and Sp. Defense.
Like Reshiram, Zekron has unique typing. Dragon and Electric is an unusual combination. It gives a 4X resistance to Electric Attacks as well as resistances to Fire, Water, Grass, Flying, and Steel attacks. The downsides are those weaknesses to common Ice and Dragon attacks, as well as a troubling Earthquake weakness. Still, combined with its stats, Zekrom can switch into a number of attacks fairly comfortably, making it a good Choice Item Pokemon.
Unlike Reshiram, Zekrom doesn't get as much wonderful coverage. Dragon and Electric are stopped cold by Steelix, Ferrothorn, and Magnezone/Magneton. All of these Pokemon have high Defense as well, making it harder for Zekrom to hit them with its better offensive stat.
Now for the good stuff: Bolt Strike. Its Zekrom's signature move and its most powerful attack and has a decent chance of paralysis as well. Easily the best electric attack in the game. It also gets Outrage, another powerful attack, though it has the problem of causing confusion. Dragon Claw is a weaker option for people who don't want that confusion.
Its physical movepool is pretty lacking for an Uber. Pretty much all that's left that is usable are Crunch, Stone Edge, and Zen Headbutt, and supereffective hits from those attacks are weaker than STAB Bolt Strike. It also has a serious lack of boosting moves. Hone Claws is all it has for the physical side of things, although the accuracy boost is nice for Bolt Strike.
Zekrom fares a bit better on the special side of things. Thunder in rain is obscenely powerful and awesome. Draco Meteor works well, too. It also gets Focus Blast, which, while inaccurate, hits the few Pokemon that do resist its STAB hard. It also puts a huge dent into T-Tar, who likes to switch in to get rid of rain and suck up attacks. Charge Beam is good for boosting, but it doesn't gel well with Draco Meteor, so Dragon Pulse will have to do in that case.
My Zekrom uses this set.
Timid Nature (+Speed, -Attack)
Not the best nature, since I don't usually play with Ubers, but it gets the job done. Use Hone Claws and then sweep. Bolt Strike and Outrage do most of the heavy lifting while Focus Blast takes care of the Pokemon that resist that combo. Lum Berry protects from status and the self-confusion from Outrage.