angry monkey said:
What about with an unarmed strike?
I say no.
You can trip with a weapon, if it's a weapon that states it can trip. If you don't have a weapon that states it can trip, you can trip someone as an unarmed attack that provokes an AoO.
The description of the weapon, unarmed strike, does not say it can trip. Therefore, if the weapon you are using is unarmed strike, you can't use it to trip; instead, you trip as an unarmed attack that provokes an AoO.
Since this is a Trip
not using a weapon, you are attacking with neither an unarmed strike nor a special monk weapon, and therefore can't do it as part of a Flurry.
If you're tripping with a kama, on the other hand, you're attacking with a special monk weapon... hence, flurryable.
Which of these actions cannot be performed with a monks flurry?
disarm
feint
grapple (ok, don't answer...)
sunder
trip
Disarm, no problem, with an unarmed strike or special monk weapon.
A feint is a standard action (or move action, with Improved Feint). Can't be part of a Flurry.
Sunder... well, that's debated. According to the table of action types in the PHB, it's a standard action, so it can't be part of a full attack action, and hence can't be part of a flurry. (It's not Action Type: Varies, and it doesn't have footnote 7.) The FAQ gives a reason for it being listed as a standard action that doesn't hold water, but goes on to say it
can be part of a full attack action (which would mean it could be part of a flurry, if you're sundering with unarmed strikes or special monk weapons).
Trip - if the weapon you're using is a/ a weapon that can be used to trip, and b/ an unarmed strike or special monk weapon. From the PHB, that means 'kama'.
-Hyp.