Serial Experiment Lain first, Texhnolyse second... Okay, maybe they're too much ! Then Ergo Proxy.
Also, i recommend Noir, maybe El Cajador de la Bruja, but absolutely not Madlax. Yes, it's from the 2000's "mainstream but in the third league", but it's fine ! Also, light yuri subtext, fuck yeah. I don't know why, but the Bee Train's trilogy is something dear to me. It's interesting to see three animes so similar yet so different !
The trashy stuff recommendation : Mnemosyne no Musume-tachi ! It's good for what it is.
Also, less trashy, but more cool : Agent Aika !
Also, i recommend Noir, maybe El Cajador de la Bruja, but absolutely not Madlax. Yes, it's from the 2000's "mainstream but in the third league", but it's fine ! Also, light yuri subtext, fuck yeah. I don't know why, but the Bee Train's trilogy is something dear to me. It's interesting to see three animes so similar yet so different !
The trashy stuff recommendation : Mnemosyne no Musume-tachi ! It's good for what it is.
Also, less trashy, but more cool : Agent Aika !
The OP and ED are quite nice too.