There's quite a bunch. Me and my friends have done about 25 over the years, but 80% are not state maintained trails, and some are *off-limits*. One required us to get a helicopter rescue (free ride, yay!). I wouldn't consider most to be dangerous though... done Haiku Stairs in a rainstorm and no injuries or close calls, and it's supposed to be dangerous.
Olomana's 2nd-3rd peak is pretty dangerous, so is most of the Ko'olau Mountain Range's ridge, especially from Mt. Olympus past H3. Windy, foggy, narrow, and precipitous. Some's not even been attempted before.
All of the waterfall trails are pretty harmless - Manoa, Maunawili, Likeke, Waimea, Laie... Sacred Falls being the exception for the chance of falling rocks.