I need a list of twitch shooters
 

In the vein of 1943, R-type, and raiden.

Einhander (PSX) was brilliant, but it's hard to find.

Which means that there are probably some used copies readily available on Amazon or eBay... for like $100.

aero fighter 1 and 2 were awesome

Anything at all in the genre?
So looking for things like Ikaruga, Psyvariar, Gunbird, Giga Wing, Mars Matrix, Trizeal, XII Stag, DonPachi, DoDonPachi, Armed Police Batrider, the entire Gradius series.

Or things a bit easier like Steel Dragon EX?

Off the top of my head that is.