marasy8 is probably my favorite YT pianist, and the only one I've subbed to. He plays mostly Touhou and Vocaloid arranges, though you'll find some Beatmania and original songs in there too.
Here's Cirno's Perfect Math Class, heh:
And From Y to Y, my favorite Vocaloid song:
I've also subbed to a guitarist, who plays mostly solo acoustic arranges of video game songs, with a few anime songs thrown in.
Tabi no Tochuu (Spice and Wolf OP):