The Bad Elf GPS Receiver plugs into your iPod touch, early generation iPhone, WiFi iPad or iPad2, allowing you to start using your beloved iOS device for navigation and all sorts of geo-goodness. I’m not yet an iOS user (though an iPad 2 is on my wish list), but the Bad Elf is so popular that I thought it deserved a post. As I compose this, it’s ranked number 23 on Amazon’s GPS bestseller list and has been in the top 100 for 147 days.