Sega recently introduced Samauri Bloodshow to the App Store. It's a weird mix of strategy and action. It's a samurai game, of course, so you're controlling samurai warriors in feudal Japan. And the actual game mechanic is sort of Plants vs. Zombies or tower defense-inspired -- you place troops out on a board, where they stand in place until enemies show up, at which point they cut them down as quickly as possible.
But the mechanic of how you lay the troops down is the weird thing -- there's a sort of collectible card game feel to it. As you level up through the game (and you can play multiple difficulties on each level), you earn cards that get added to your deck, and it's those cards that actually summon the samurai. It's an interesting mechanic, but it's a little out of place, and unfortunately, the game's translation issues make things a little confusing.
That said, there's plenty of content to play with here, with over 100 levels to go through, lots of cards to find and collect, and full Game Center integration as well. Samurai Bloodshow is US$4.99 on the App Store right now.