Those are mainstream just as well. I think DualStorm was just talking about the American mainstream. Here's just a few, not quite so mainstream I could recommend you to watch:
Baccano! (something I can't really describe with just a few words)
Sakigake!! Cromartie Koukou (one of the best gag animes there is)
Darker than BLACK - Kuro no Keiyakusha (neo noir anime about people with supernatural powers, but darker than most with the same theme)
Kaidoumaru (beautiful historical anime, one episode OVA)
Kaiba (romantic scifi, a little different kind of anime)
Kamichu! (slice of life anime about a girl who became a kami)
Kino no Tabi (episodic style anime about travels of Kino and a motorcycle Hermes)
Megazone 23 (old three part cyberpunk OVA)
Nekojiru-sou (a surrealistic anime movie about two cats, based on a gag manga/anime)
Samurai Champloo (adventure comedy, a little different kind of samurai anime)
Shinreigatari (supernatural stuff)
I was just bored.