I am a 'YUGE meganekko fan. I don't know why, but I often find them to be the more interesting of anime trope characters, especially when they know how to work them glasses. I also have too many favorites to list, but I will keep it to my current top three. (Hmm, some have already been mentioned, but here goes...)
(3) This one is a bit different for me. Mari Illustrious Makinami from the Evangelion
reboot movies. As insanely blood-thirsty as this girl can be when piloting an eva, with her wearing those cat-eye glasses while doing so just inverts her cocky, vicious attitude, which to me is usually off-putting, and makes her seem, yeah, sexy. It's just glasses, mind you, but, hey, it works. Cannot for the life of me explain.
(2) I don't think anyone has yet mentioned Mirai Kuriyama from Kyoukai no Kanata
(Beyond the Boundary
). She's easily one of the top ten, and she's so incredibly adorable. She fits the trope to a tee, as only Kyo Ani can.
(1) BUT my top pick for all-time best meganekko is, of course, the poster child for this forum question, Tsubasa Hanekawa from the Monogatari
series. "I don't know everything, Araragi. I only now what I know." Long hair, braids, or short hair, she's adorably hot and witty and cute. I did feel a bit betrayed when in later seasons she started wearing contacts, but I was already smitten, so I can overlook that. Also in her favor is that her aberrational form is that of ferocious cat-girl. A Mega Neko, or "Big Cat", if you get the pun.