Serial Experiment Lain is a really, really twisted series. In the first episode of the series, Chisa, a girl from Lain's school, mysteriously commits suicide. Then, Lain receives an e-mail from Chisa telling her to let go of her physical body and join the world of the Wired. After that, Lain's father buys her the newest NAVI computer, and she finds some kind of chip, and the boundry between the real world and the Wired gets rather fuzzed up, and it gets a lot weirder from there. And then she has that really creepy smile too.
I really like the series -- it reminded me of a weird mix between Evangelion and Key the Metal Idol. I also like the art. A lot of soft and fuzzy colors are used, creating an almost dream-like environment. Definately a good series to watch, but only if you enjoy weird techno stuff.