Chobits is a decent suggestion, given responses so far. It is, ultimately, not as intelligent as it thinks it is, but it's still smarter than most.
What I reach for when I want a YKK vibe but need something licensed is Aqua / Aria -- one series, renamed when it changed publishers, though as the anime is called Aria that's usually taken as the franchise name. It doesn't have the depth of thinky -- the anime, oddly, has more than the manga -- but the atmosphere is similar, and as the series progresses the weirdness gets deeper.
Another in the YKK vein is Ai-Ren (available here on ST) -- not as long, but similar themes and more romance.