Maxar

Can't go wrong with Crimzon Clover. It's pretty much explosions: the game, in a good way. Also quite a bit harder than Touhou.

The C81 version of Stella Vanity is really nice if you like complex game mechanics (three shot types at once, two different hyper modes, equippable items, gaining levels).

Exceed 2nd and 3rd are heaps of fun. The former has an Ikaruga style polarity system, and the latter is just a really solid Touhou-style shmup.

RefRain is of very high quality (but easy).

The Gundemonium trilogy (Recollection, Gundeadligne and Hitogata Happa) is solid. The first two are horizontal shooters but otherwise very much bullet hell, the third is Touhou with a suicide bomb mechanic.

Ether Vapor (the remastered version) is amazing, at least visually. Do tell if you figure out what exactly your hitbox is in that one.

And if you're feeling particularly masochistic, many CAVE arcade games can be emulated on M.A.M.E.