Sesshoumaru is one of my top ten cuties that his personality adds to his cuteness. Unlike Chris who is just plain cute,
Sesshoumaru has inner beauty. 
He is the ultimate straight-faced guy--I love that. You will never see him with a goofy face or a face filled with fear.
Even when his life is threatened, he remains cool and collected. Sesshoumaru has one of the most beautiful faces I have seen animated. The cresent moon on his forehead,
his golden eyes, the two scratch-like marks below each of his eyes, and of course his nearly perpetual neutral expression--I adore his face. Oh, and his long white hair is just so much more
appealing on him than Inu Yasha. On Sesshoumaru it makes him seem dignified; Inu Yasha just looks like he let it grow because it would be too much trouble to cut it (or maybe Michi's just a bit biased, hehe ^_^).
If it wasn't
enough that Sesshoumaru looks great and has this wonderful serene personality, his voice is incredibly sexy, not to mention his manner of speaking. That's why when I listened to his dubbed voice I thought it robbed him of the aloof tone he usually has with everyone. There's a particular moment when you can actually hear Sesshoumaru's seiyuu's (whom's name escapes me right now) tongue moving as his articulates his words. I can't remember the episode number, but it is after Sesshoumaru takes the sword he inheirted from his father and slashes Jaken in half to prove that the sword can't kill. Then after Jaken is laying on the ground in shock Sesshoumaru says, "Nani o shiteru? Okiro (What are you doing? Wake up)." It's the "shiteru!" You can hear how sexily he pronounces that word! Oh, I love it! Plus, as I mentioned earlier in this paragraph, Sesshoumaru has this incredibly appealing manner of speech. First of all he uses "watashi" to address himself, which to me is somewhat a more bishounen way to address oneself. It just sounds better than "ore" and not as "fruity" as "boku." Anyway, Sesshoumaru, not like many anime characters I have noticed so far, often refers to himself in third person. Why, once he said to Naraku "Mokuteki wa kono Sesshoumaru no inochi ka (Your intent is this Sesshoumaru's life)?" I absolutely love when he does that. I mean, audio-wise Sesshoumaru's got it all--a sexy voice, appealing speech, talks in third person. Yep, you can often find me just sitting on the computer listening to his words.
Summing up what makes Sesshoumaru easily get on my best bishounen list is that even when he loses his cool and gets angry (even when changed into that beast thing), that doesn't take away his beauty one bit. Sometimes I want to see him angry, just because it's a lovely contrast. If he were scowling all the time, however, I don't think I would consider him so cute. I've seen up to episode 87 of Inu Yasha and I don't think he has nearly enough screen time. I'd much rather watch what Sesshoumaru's doing than Inu Yasha. ^_^