Aleste/Power Strike 1&2 on Master System, still play them on original hardware. MD and SNES Aleste rule too.
Skonec games, they've got real flair when it comes to bullet patterns.
Gradius V, my favourite Treasure game.
Illvello, love everything about it favourite Milestone title for sure.
Raizing stuff of course.
Triangle Service games, the compilation on 360 was too good.
edit: this one's an odd inclusion but I quite like meta-ph-list on ps1, its bad but I couldnt stop playing it, even had a go with the mouse.