I want to know what makes a rpg qualify as hardcore. Difficult? Traditional? Dark? Mature? Manly?
EXTREME? I mean,
almost anything could qualify as hardcore if you stretch the definition far enough.
Front Mission 1 (SNES, DS) and 3 (PSX) are SRPG favourites of mine. Both have detailed worlds and good storylines with political and personal conflicts. Both have 2 main storyline paths, basically easy mode and hard mode, and even easy mode is fairly challenging. Both are fairly gritty without being over the top about it. A little bit of tedious micromanagement upgrading units, but this is the DF forum after all, it's nothing you can't overlook.
7th Saga for SNES gets honourable mention for being stupidly difficult for absolutely no good reason, if that's what you're looking for. It's not the highest quality game overall though.
Valkyrie Profile : Covenant of the Plume (DS) is another SRPG and definitely hardcore. In fact it tries way to hard to be hardcore, but it's still fun. The game revolves around making a pact with a demon (or something, I don't know), in which you can murder your own teammates and steal their souls for buffs. Battle strategy is generally to surround and gang-beat opponents into bloody pulps to accumulate OVERKILL BONUS. It also gives the choice between more and less difficult story paths.
The PC recommendations in this thread are all good. Baldurs Gate and Fallout series, Arcana, Planescape, etc. Never was a fan of the Elder Scrolls games but everybody else seems to like them. The SNES, DS, and PSX/2 all have a huge library of quality RPGs, if you have the hardware. Used PS2's and DS's are dirt cheap now too, I recommend investing.