TruePower IV Pro 3100 mAh Mobile Charger for iPhone/iPod
Love this product.  I don't know how anybody who has an I-Phone  goes without.  It keeps me up all day even with heavy use.  It works for  both my I-Phone 3 and now 4.   With my True Power battery, I do not fear  to use my phone as I know I have enough batter. - GREAT PRODUCT