I really like the sound of Justice Heart on Lucario, especially on an Agility set! Lucario typically runs into problems with the likes of Gliscor, Choice Scarf Tyranitar / Garchomp / Magnezone, and various other Pokémon, which Agility solves. With a 4x resistance to Dark-type attacks he can switch-in on a move like Crunch (typically seen on Pokémon like Tyranitar), gain +1 Attack thanks to his ability, then set-up an Agility on the switch. You then have a +1 Atk / +2 Spe Lucario on your hands, ready to wreak havoc.
Lucario @ Life Orb
Ability: Justice Heart
Nature: Naughty
EVs: 4 SpA / 252 Atk / 252 Spe
-Agility
-Close Combat
-Crunch
-Hidden Power Ice
Pretty straightforward set. Naughty is chosen over Adamant so HP Ice doesn't receive -SpA; I don't think Luke can use Ice Punch in B&W :/ With a Naughty nature, you reach a speed stat of 558, which is enough to outrun the likes of Choice Scarf Garchomp, giving you an opportunity to clobber it with HP Ice. You also reach an attack stat of 525 if you manage to get a boost from Justice Heart. Pair this up with a few entry hazards, and you've got yourself a monster. Also, as far as I know, Dream World abilities can be breed, so I think it's possible to have Crunch and Justice Heart on the same set. Correct me if I'm wrong.
Swords Dance sets also gained a huge boost, seeing as ExtremeSpeed is now +2 priority, which means Mach Punch Infernape can't revenge kill you now! Also, if Justice Heart is compatible with the typical moves Lucario runs on an SD set, that's sweet. If you get an attack boost from Justice Heart and a SD under your belt, you'll have a +3 ExtremeSpeed to wreck stuff with. Absolutely beautiful.
Lucario has access to pretty much all of the major stat-boosting moves, which is pretty cool. I'm excited that Luke obtained Nasty Plot in Generation V, since it gives Luke a viable way to make use of its stellar Special Attack stat without having to resort to using Calm Mind or Choice Specs. A +2 Vacuum Wave is incredibly useful for killing off faster Scarfers who are weak to the move. All in all, I'm pleased with the improvements Lucario got in B&W. Let's see how well he'll fare in the Gen. V metagame!