Gun Frontier has an amazing OST by Zuntata. Most memorable and unique track for me is the Stage 2 music. It starts out peaceful and quiet and keeps building up with the action!
Rapid Hero / Arcadia - Stage 2 music - totally over the top and epic - just like the game itself!
J.J. Squawkers - Stage 2 music (again) - Probably the most relaxing arcade track in history

Breaking the stage 2 streak with one of my favourite CAVE shooters:
Mushihimesama - Stage 3 music. Almost has a Prog Rock sound to it. Music suits the stage perfectly! Love this track.