The built in one rocks. If the phone's locked/sleeping, double-tap home and tap the camera icon. Comes on quickly, use the "+" volume button as a shutter, supports real HDR, puts them both on the roll and Photo Stream (wirelessly sends them to iPhoto and other iOS devices).

Huge pictures:
http://farm7.staticflickr.com/6155/6...435da79b_o.jpg
http://farm7.staticflickr.com/6052/6...609cdeee_o.jpg