I have a few builds I've tested that have a lot of synergy with one another, and I figured I'd share here and ask for really cool combinations that you guys have found as well. I have mostly tested quarterstaff builds, so those are the ones I'll be posting:
12 Monk/8 Rogue
30% Sustained attack speed in GM Wind stance, 60% with action boost.
+8 Attack/+16 Damage on a 17-20 3x Crit weapon (QStaff)
All sorts of nifty skills, like a mass trip
Tons of Sneak Attack
Can go DEX based for a lot of bonuses/trip DC bonus on sweeping strike
Henshin Anti-Dark/Light Move/Void Punch/Access to all finishers
12 Bard/5 Rogue/3 Barbarian
All self buffs
4x Crit with Quarterstaves while under 50% health (5x with Imp. Critical) (Occult)
Barb/Bard rage synergy
All the cool sweeping moves
Can go DEX based (Though STR would be better for Imp. Critical)
14 FvS/6 Monk (Drow or Halfling) (Shortswords)
DEX to shortsword damage
Easily integrate shuriken throwing for some lulzy shortsword+thrower builds
Self Buffs/Aoe Damage/Huge self heals
Grandmaster stances- large amount of doublestrike
Trying to find weirder combinations like Monk/Arti.
But post your ideas and have fun with this.
Let's bounce ideas off each other and see if we can find any other cool combinations. I'll update this main post with the ideas and whoever they are credited to. Don't count out class or racial bonuses!