If you're like me, the default white glossy square icon that newly created iOS apps use might bug you a little. There's nothing like a proper icon to really make your project feel that much more official and polished but making good icons takes time and it's not really something you want to fiddle around with early in development. But it's not too hard to make a good placeholder icon thanks to the emoji font that ships with OS X Lion, let me give you some examples.
These icons are crazy easy to make, just a gradient and an icon, iOS handles rounding the corners. If you're not sure how to type emoji characters, just select Special Characters from most apps' edit menus or type ⌥⌘T to open the special characters pallet and choose Emoji from the sidebar there.