I downloaded Gunstar Heroes and SIn and Punishment today... Gunstar Heroes is pretty fun. It's basically a side scrolling shooter, so if you're into that, by all means check it out.
Sin and Punishment is another great game. I have to thank Hanz for recommending it. :P
There's a 'Popular Titles' tab in the shop channel, if that's any indication. Otherwise, you can go to Nintendo.com to check out a gameplay video of the title you're looking for, though they're only like, 30 seconds long. If that fails, you can always go check out reviews for the game.