
No one knows the forum quite like you do, Bernhard...
I don't think I can add much after that, but if I were you (Mosis) I wouldn't let the "difficulty" of a piece put you off wanting to learn it. I would list ALL of the pieces you like and want to learn regardless of difficulty. Then if you like, you can even have a "bit of fun" every now and then and start chipping away at the more difficult pieces just bit by bit and within a few years, you might have one of them ready to go!
As for finding "obscure" composers, one of the best things to do is go to a well-stocked CD store (in America/Houston they have "Borders"--I haven't seen one elsewhere but I suppose it doesn't mean they don't exist outside of America...anyway if you're in America it's a good store) and just spend a few hours looking around all the composers and seeing what catches your fancy. I like Borders in particular because they have systems with virtually every CD--minus the super obscure ones--in a database with 45-or-so second samples from each track.
What ends up happening when you get in the classical sections of the stores is you'll stand there, intimidated at first and not knowing where to start..then you begin brainstorming..."which composers have I heard about, but haven't *heard*? I've read a lot about Alkan on the forum but I've never actually heard his music..." and so forth...so you look for Alkan, play some of the CD...then another name pops in your head...and you get going that way. Eventually you'll start seeing things "out of the corner of your eye" in sections next to those you're looking at and before long, you've found a completely "new" composer that you absolutely love. That's how I found out about Durufle--well, I was looking for Donyanhi and found Durufle instead in the D section. But had I not spend an hour or so skimming through all the CD's, I never would have found Durufle's hauntingly beautiful Requiem Mass.
So, in short, it just takes an open mind and a lot of experimentation. Sometimes it comes down to closing your eyes and picking a CD completely at random...just as long as you expose yourself to something new. Eventually, you'll find some great pieces that you originally knew nothing about and that you want to play.
To start you out a little, I'll through out a few names: Alkan, Busoni, Godowsky, Couperin, Gibbons, Byrd (the last three are from Baroque or earlier), Mahler (not too obscure but definitely worth it), Scriabin, Glazunov, Balakirev (look beyond Islamey!! Find his mazurkas and concerto), Donyhani (if you can spell that right you're on track...I don't think that sp is correct), Ornstein, Schoenberg, Webern, Moszkowski (true gems), Haydn (more neglected than most think), Liszt (same as Haydn), Bolcom, John Field (remember: he didn't JUST write nocturnes), etc. etc.
None of those are *too* obscure but they're all definitely worth looking into.
Also investigate pianists you've heard about but never gotten around to listening to. Sometimes, you'll not only be surprised by the pianist (good or bad) but you'll consequently be exposed to tremendous music that you'd never thought of before--or at least, you'll hear music played in ways you never thought it could be played and end up liking stuff you didn't before, etc.
I'd personally recommend trying any pianist that remotely interests you in any way but maybe you could try looking specifically for: Horowitz (a "duh" moment--but, really, dig into his CD output for some great performances), Andras Schiff, Glenn Gould (definitely look beyond the standard Goldberg Variations), Georges Cziffra, Marc-Andre Hamelin, Yudni Li, Arcadi Volodos, Kapell, Brendel, Goode, Kuerti, Moiseiwitsch, Argerich, Zimmerman, O'Conor, Firth, Pogorelich...you get the idea.
Anyway, I hope that starts you off. Just buying those recordings and slowly expanding your knowledge of the literature is great (I try and aim for "a new CD a month" just as a bit of a goal). From then on, you'll have a greater understanding of what's available and you can decide from there what you want to play and what you can play, etc. etc.