Cincinnatus: In this—as in all incarnations of Superman—Clark has the power to amass great power and wealth if he chooses too, and could easily be the world's most feared villain due to his sheer power, but instead chooses to fight for Truth, Justice, and the American Way.
Corrupt the Cutie: Quite a few have attempted to do this; all have failed miserably and often end up on the receiving end of a hilarious put-down by Clark.
Good Is Not Dumb: As Superman, occasionally. Comes up with his more intelligent but vain foes who think Superman can be simply maneuvered around, such as those involved with Intergang. Occasionally, he runs into characters who think they take advantage of his honor as if it were naivete, but as Clark is quite quick witted he is easily able to Take a Third Option.
The Casanova: Has tons of women lusting after them—and he happily beds them—but he considers all of them trophies. The only one he actually wants for something more than a mere one night stand is a certain crusading reporter...
The Chessmaster: And he's frighteningly good at manipulating the entire population of Metropolis like pieces on a chessboard.
Graceful Loser: Of a sort. He has an uncanny ability to see the silver lining in defeat, and even when he can't he barely ever shows rage or pettiness or acts with anything but grace - perhaps because he believes that ultimately he will be victorious. For example, his reaction upon learning that an unstoppable virus is rampaging through is systems and may ruin him (and the world) is to have a cheerful discussion about philosophy and getting back to nature with his butler, and stays chipper even after he concludes that he would absolutely hate it. Whenever Superman beats him, he essentially shrugs, tips his hat and goes on to other schemes. But on the other hand, when all of his plans go horribly, horribly wrong, he has a quite more pronounced reaction.
Vague Age: He seems to be in his late 20s or early 30s, yet he somehow has children who are apparently middle-aged. It's possible he's Older Than He Looks.
Actually brought up by Clark in a Season 4 episode dealing with the aforementioned children. Lois questions how Lex could have kids so old, and Clark replies that Lex was such a Magnificent Bastard that his official age could very well be faked; thus the show seems to be implying that Lex is indeed Older Than He Looks.