These are bands that have piano, not synth. Of course, it's probably a keyboard making a piano sound...but it's still piano.
Arcturus has a bunch of songs with piano as opposed to keyboard.
I second Winds.
Devil Doll has a lot of piano work, as it is mostly classically based.
"Om Hundrede Aar Er Alting Glem" by Borknagar is a piano instrumental.
Dream Theater also has songs with just piano.