Soldner-X 2: Final Prototype plans on hitting the PlayStation Network on May 25th for $12.99.  With it you get a side scrolling shooter with a handful of game modes including two player local co-op play.  

The Original Söldner-X: Himmelssturmer has possibly the longest and hardest name to say for a side scrolling shooter ever.  Seriously, it sounds like you have a mouth full of hot taco beef and tried to recite Shakespeare.  But there's a sequel now, one that isn't as hard to pronounce, it's called Söldner-X 2: Final Prototype and it's an upgrade from it's predecessor in a handful of ways.