okami - one of the most imaginative, artistic, inspiring games...ever. better than windsailing zelda(not ocarina of time or a link to the past though)
katamari damacy or we love katamari - simple addicting gameplay topped with "delicious" sound and visual design.
ico - the emotional connection that the game creates is just pure magic, too bad that most gamers can finish it in one sitting though.
final fantasy 12 - best jrpg i have played in long long time.(actually that might be due to the fact that i don't play that many jrpgs anymore more )
mgs 3 - big production values, the insanely detailed design (visuals, game mechanics,characters,extras..etc), and uncontainably cheesy yet addicting kojima team flavor that million of gamer crave.
actually i should add shadow of the colossus to my best ps2 games evarrrr list too. The originality of its gameplay concept, the soundtrack(easily one of the best game soundtracks of all time), and the artistic/inspiring visual design makes this game one of the most memorable ps2 games that i have owned.