Combining factotum with iaijutsu master, to capitalize on cunning surge with one strike, two cuts, I'm looking for a way to hit multiple enemies with each standard action's attack. For a human character, are there any feats or 1 to 2 level class dips that can make this happen? If so, which?
One strike, Two Cuts already can hit two people. It's two attacks, not two attacks on the same target.
The only thing other than Sweeping Strike that will add an extra attack to standard action directly is Snap Kick. That will mean 3 attacks per standard action. It requires high bab and unarmed strike.
Otherwise, Improved Trip + Knockdown will generate an extra attack if the trip is successful. Lightning Maces + an Aptitude Katana and an Aptitude Wakizashi will maybe generate extra attacks. Karmic Strike, Retaliation, and/or Robilar's Gambit will also generate extra attacks when combined with Combat Reflexes, although not as part of that standard action.
Decisive Strike (Monk Variant) will allow you to double your damage with a full round action attack for the entire round, and then Cunning Surge/Gambit/Trip/Snap Kick to get more attacks all at double damage. A Passive Way (UA) Decisive Strike (PHBII) Monk 2 gets Improved Trip as a bonus feat as well as decisive strike. An Invisible Fist (Champions of Ruin) monk can be added to that to trade evasion for natural greater invis 1 round in 3, which helps with the whole 'alphastrike murderer' vibe.
As a slightly less cheesy version of the 'bag of rats fighter', you could take Great Cleave and then have kill squads of first level goblin ninja suicide commandos who run in with you and get cleaved by you with a whirlwind attack or similar (there are weapons that give you a /day whirlwind attack) and then each generate a free attack, which you could fluff as them running forward as bodyshields, and you cutting through them to deny your enemy the chance to dodge. Which is very doable for a 18th level character or whatever the hell (Factotum 8/Iaijutsu Master 8 = level 16, i.e., nearly 9th level spells).
That's all I can really think of that could help you out.
The only options I am aware of for attacking multiple enemies with a standard action are Iron Heart’s steel wind, mithral tornado, and adamantine hurricane maneuvers, and the war mind’s Sweeping Strike feature.
A standard action to attack two enemies, as with the Iron Heart maneuvers, won’t actually work with One Strike, Two Cuts, however. One Strike, Two Cuts is not an attack action, nor does it trigger when you take a standard action that attacks, it’s a specific unique standard action. No other standard action is going to work with it; you would have to choose, e.g., between One Strike, Two Cuts and mithral tornado.
On the other hand, Sweeping Strike works on any melee attack, and therefore actually combines with One Strike, Two Cuts (or the Iron Heart maneuvers, for that matter). Each of those attacks can hit two targets. It also doesn’t happen until War Mind 5th, and that class is not particularly well-suited to your build, being Wis-based while you’re already split on Int/Cha. But I do not believe any other official material will work for your goal on a regular basis.
Your next-best option is to just take Cleave. It won’t trigger often at all, but it will work. I do not actually recommend this; it’s just so rare that you’ll get to cleave in a situation where it’s important.