Can you guys list some great shoot 'em ups?

I know the Raiden, Metal Slug, Contra, Gradius, Space Invaders, Galaga, R-Type series, and I've played some Treasure games.

I'm mostly looking for Vertical Shooters (Raiden, Ikaruga), Run and Gun (Metal Slug, Contra, Gunstar Heroes) or Horizontal Shooters (R-Type, Darius). On-Rails are fine too.

Einhander (PS) and Life Force (NES) have crazy boss designs....such as a big robot gorilla and a brain with arms.