"Hardcore" Gamecube Games

[fast]

Resident Evils
Eternal Darkness
Blood Omen 2
Bloodrayne
BMX XXX
Geist

[vash23n]

Don't forget Timesplitters 3: Future Perfect. A lot like Timesplitters 2, but some pretty awesome new levels and just as hard. Rated M I am sure. Second Sight is another game by the same developers that I have never played, but is supposed to be pretty great.

[fast]

Second Sight looks neat, I have never seen it in stores though.
Killer7 is another you might want to look into.