A Space Shooter (for free) used to be a space shooter for a few more dollars, but the developers decided instead to bring it down a freemium level, which means you can pick up this quality arcade title for free. Not only does the game offer plenty of solid shooting action, with lots of enemies and pickups, but there's a surprisingly good story here, too, told through cutscenes full of pretty funny (though occasionally grating and even a little racy, I'll admit) dialogue.
But the shooter action is fun. The game does suffer a little bit from the issue that all iOS shooters seem to have, which is that your finger often gets in the way of seeing just where your little ship is supposed to be. But fortunately the game uses a health meter rather than a one-shot kill, so while you might still clip the occasional enemy, you'll probably be fine anyway.
There's full OpenFeint and Game Center integration, and in accordance with the freemium model, there are plenty of in-app purchases to make if that's what you choose to do. But A Space Shooter for free is a solid iOS game, and of course the price is just right.