Lucario's kill moves (at 100%ish, just kind of going off memory here):
Usmash, Dsmash, Fsmash, Utilt, Fthrow, Bthrow, Bair, Dair, Uair, NeutralB, DownB, SideB(grab) and that's assuming you don't fair/nair offstage to gimp a recovery.
Lucario has the unique trait that his own % matters so I'll go through these with a bit more detail.
Dsmash and Fsmash: Both one of Lucario's best actual KO moves. They kill better then anything else at lower percents. Also note that all aura attacks (I think) sweetspot at the tip. I've heard my friend complain that a sweetspotted Fsmash killed him at 60% while Lucario was at 50%.
Usmash: Same as the other smashes but not as effective against heavier characters
Utilt: Kills at surprisingly lower %'s against light-weight characters
Fthrow: Grab > Fthrow can be done almost instantly, kills at decent percents
Bthrow: Not effected by aura boosts, so if you're at low % and your opponent isn't...
Bair, Dair: May not be the best KO moves in the game but at higher %'s these are just as lethal as any smash attack
Uair: Kills light/midweight characters best
NeutralB: Very leathal
DownB: On average, when Lucario is at 100%, Double team will at roughly 109% and under 100% when Lucario is above 150%
SideB(grab): Without DI it's a very good killer, with DI it takes a little more.
Now I know that a lot of these don't look like the best kill moves since they kill at 300% from the center of FD but lets face it... When do we ever drag our opponent to the center of FD just to use a KO move? Also keep in mind Lucario's off-stage game is amazing. He can WoP and even finish it wit ha dair/nair for an extremely low % kill. Even a single fair can kill or Lucario's upB to edgehog.
My advice, don't just focus on Aura Spheres. Lucario has a ton of options, try a few things, eventually one will work. Against lighter characters I suggest any upwards attacks. Utilt is fast and combo's into itself at low percents and kills at higher. Usmash is nice... just don't miss, Uair is great, just keep juggling them until you can jump high enough to KO them with it.