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"rRootage":

Summary: Fine port of the Kenta Cho shmup classic.
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"Sentry Alpha":

Summary: A retro Xevious-esque vert.
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"iFighter":

Summary: A Strikers 1945 inspired vertical shmup.
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"Sky Thunder":

Summary: Slightly Toaplan-esque vert.
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"Sky Force Reloaded":

Summary: Vert with emphasis on not letting enemies escape.
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"HotField":

Summary: This one could be at home in a Sega Saturn shmup library.
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"Siberian Strike":

Summary: Lavish vert for fans of 1943, 19XX, etc.
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"Star Trek":

Summary: Loosely affiliated with recent movie, but has unusual gameplay.
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"Dragon Force Light":

Summary: Couldn't find a way to buy the full version of this (maybe coming soon), but the 1 stage demo had potential.
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"iDodge Space Ninja":

Summary: Vert where your ship cannot shoot, but must dodge attacks while pushing forward.
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"Triphids":

Summary: A Gyruss variant with a deliberately retro look and feel.
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"Galaga Remix":

Summary: A slight modification of PSP's Galaga Arrangement.
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"Radio Flare":

Summary: Hori scroller with Rez-style lock-on mechanics.
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"Space Deadbeef":

Summary: Strangely titled japanese hori shmup.
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note: this thread is just for shmups, for non-shmup iPhone/iTouch recommendations please use this thread...
I've deliberately omitted some bad titles, but it's possible I've missed some decent ones - and of course new ones are being released each week, as software development for the platform is thriving.

Edit: fixed expired image link.