I've seen blazingstar mentioned in this thread, try the predecessor pulstar. it's rumored that the original r-type designers were majorly involved and you will see why. It's awesome. I think I've worn out my sanwa buttons playing pulstar on my cabinet.
neogeo:
- pulstar
- aerofighters/sonic wings 2 & 3
- viewpoint
- andro dunos
pcengine is by far my most favorite system for playing shmups. rtype ports are supreme, but you need to get two hucards for the complete game as they split it in half.
more awesome pcengin shmups/ports:
- mr. heli
- download
- image fight
- darius alpha
- armored formation F
these two are incredibly cool:
- gate of thunder (cd only)
- lords of thunder (cd only)
on megadrive there is a couple of great shmups as well:
- eliminate down
- sub terrania
- ranger x (this one is awesome, as you play a mech with the ability to transform and fly, also very tactical gameplay, not really a pure shmup)