Prince of Persia: The Two Thrones. Goddamn troll in arena fight is killing me. The Dagger never flashes :(
If I remember correctly you have to slash the crap out of his ankles then you go on one of the sides, do a little platforming, then jump at him and its dagger time.
As for games I'm stuck on. The only one I can think of that I haven't beaten due to not being able to is:
Ninja Gaiden: Church battle with Anya. God I hate her so much.