I think all chances of 10% or lower need to be removed (not counting secondary effects from elemental fangs or Tri Attack). Rock Slide always hits (there is no other 100% accurate physical rock move besides 50 BP Knock Down, unfortunately).
Also, if Blizzard/Thunder/Focus Blast/etc. is made 100% accurate, I think the secondary effect chance needs to be the original secondary effect chance*the original accuracy of the move. For example, Zap Cannon may be 100% accurate, but only have a 50% chance to paralyze, not making it completely broken (70BP 100% chance to paralyze!?).
All moves, items and abilities that only introduce hax should be banned, obviously. (Brightpowder, Double Team, Minimize, Inconsistent, Acupressure, King's Rock, Razor Claw, Scope Lens, Lax Incense, Razor Fang, Sand Veil, Snow Cloak, Focus Band, etc. if there is anything else) However, we may need to work around some abilities, like Sand Veil/Snow cloak lowers HP dealt by 20% in Sand/Hail, respectively.
Speed ties should be like in Aldaron's thread (both pokemon move simultaneously, not being affected by the opponent's move until both are executed, assuming equal priority).
Also, we need to get rid of regular shinies. The chance of getting one is so small. :P