Jailbroken iPhones/iPod touch only: iPhone-Backgrounder, a free app utility available through the (jailbreak-only) Cydia store, makes running apps in the background seriously simple. After installing the utility, you simply hold down the Home button to "minimise" an application. Call it back up again using its app icon, and then hold the home button again to kill it off for real. Backgrounding worked with at least four apps I tested, and kept the audio playing from Last.fm while checking email or web browsing. There are bound to be a few bugs and inconsistencies, but it's a great hack for keeping music, instant messaging, and other streaming programs close at hand. iPhone-Backgrounder is free and requires a jailbroken iPhone or iPod touch (check our guides for Macs and Windows for help with that).