I know a couple, some more obscure than others;
- Blue Gender, this was one of those adult swim anime. This ones a Mecha series, personally I liked it. The animation dose have some rough spots which holds it back, and also its got a pretty rushed ending.
- Witch Hunter Robin, a show also from the adult swim period. This one is witchcraft meets police procedural. I however found the show incredibly dull and drawn out and have currently put it on the back burner,
- Wolfs Rain, this show is one of my all time favourites despite how obscure it is. It a really atmospheric show but is an easy watch and very enjoyable.
Those three I'd consider the really obscure shows I've seen however some others which aren't very mainstream but also aren't very niche and have a healthy amount of discussion are;
- Ergo Proxy, this show is very atmospheric and is in my opinion a must watch. This show is still got a little bit of an online presence amongst the Anime Community, so it not totally forgotten like the previously mentioned shows.
- Monster, I've been seeing this anime get more and more praise so it's clearly no longer obscure as it was. It a very intelligence and thought provoking show, so you've likely heard of it if not sat down and watched it however if you haven't seen it yet I'd highly recommend this show.
- Parasyte the Maxim, despite being the newest anime I've mentioned this is a show hardly anyone talks about. However if you want a dark, mature action anime to watch this is again a good show to pick up.