I Kissed a Girl, Firework are classics no doubt.
California Gurls, if it continues to age well, yes; Teenage Dream (song) needs to age well and it MIGHT in a few years. ET I don't feel could ever be iconic but instead remain one of Katy's biggest fan favorites, same with Hot n Cold: the GP wouldn't classify these 2 as classics. Thinking of You, Waking Up in Vegas, Last Friday Night, Part of Me, Wide Awake... I don't think so

they get forgotten too easily (personally, I'm most upset about Wide Awake, but alas...)
But as of now only Firework and IKAG really hold the clasic status.