Re: Obscure and Rare Anime
I have just a few:
Assemble Insert: A pretty fun little OVA from the 80's that parodies stuff like Patlabor and other typical action shows from the period. Yutaka Izubuchi shares a credit for mech design, and it shows.
Labyrinth of Flames: A very fun and echi OVA. It's about a young Russian guy who trains to become a ninja with a family of ninja that escaped to Russia after the Sengoku era.
Ruin Explorers: Was a pretty fun OVA back in the day. The ending left me wanting more though...
Hantsuki: Relatively new (Winter 2006 series), yet somewhat obscure. It was a nice tearjerker about a guy and his girlfriend who was hospitalized due to heart problems. Only six episodes, but worth a watch through.
Outlanders: This one is probably not as obscure as I think, but it was a fun classic. Alien girls and space politics, etc.
Natsuki Crisis: Old, short, OVA meant to sell manga and test the waters for an TV series. While there is a jarring transition from episode 1 to episode 2, it was fun despite being somewhat of a preview of a much longer story. About two girls who were...in some sort of fighting club at school, they develop a friendly rivalry, and have some nicely animated fights.
Combustible Campus Guardress: Though I never got to see all of it, what I did see was some nicely animated 90's fighting anime. It was crazy, but fun to watch. I'm not sure as to how hard it is to find, but I can say it's pretty obscure.
That's all I can think of for now. Hope those help!