I don't know of very many two-player shooters.
The only ones in the US are Ordyne and Aero Blasters. Forgotten Worlds has the lame satellite mode, Falcon is a two-player flight simulator on TE, and Soldier Blade has two and five minute competition modes. Finally, Galaga '90 allows two controllers to be plugged in but you both control the same ship. Weak.
Besides Psychic Storm, Sapphire is excellent. Is 1941 two-player?