I never owned a PS2 so I have picked up a few PS2 games and they are superb - they look great when upscaled once you get used to them (they are obviously noway near as crisp as HD). I own the following and they all look great (especially GOW2):-
God of War
God of War 2
Final Fantasy 12
Dragon Quest 8
In fact I play more PS2 games than I do PS3 (with the exception of the sublime Oblivion)!