Timid (+Spd., -Atk.)
Unnerve (Opponent can't use Berries)
Center around Sp. Atk. and Spd.
ElectroWeb (55/95/15, Drops enemy Spd. 1 stage)
Agility (-/-/30, Raises Spd. by 2 stages)
Electro Ball (-/100/10, Damage based on Spd. comparison)
Energy Ball (80/100/10, 10% chance of dropping enemy Sp. Def. by 1 stage)
This setup is specifically for fully utilizing the effect of Electro Ball (which does damage based on how much faster Galvantula is than the opponent). It wil start off with either ElectroWeb (if it needs to go ahead and deal some damage) or Agility (if it's up against a more defensive opponent). After using these moves a few times (mostly Agility, since it actually affects Galvantula's Spd.), you can start hammering away with Electro Ball.
Energy Ball (TM53) as the last move gives it some cover in case it comes up against a Ground-type (which Electro Ball won't hit) or a Rock-type (which it is weak to). Being EV'd toward Special Attack will help this move get some power since it won't receive STAB. The Occa Berry will protect it from a Fire-type hit once, but then it's susceptible to Fire from there on. Having the Berry and Energy Ball help get around its two elemental weaknesses (Fire and Rock).
If the opponent has a really fast Pokemon (especially a Fire-type), this may lose some of its usefulness. Also, Galvantula has relatively weak defenses, so it needs to get in and set up quickly before it gets taken out (I'm currently in the works on both Single and Multi Battle solutions to this).
Sorry this has been so wordy, but I figured I needed to say what its purpose was. Also, I'm not good with EV and IV stuff, so if someone wants to help with that, I'm all ears.