The Monoprice Backup battery pack is the simplest of devices. When your iPhone or iPod is running low on juice, just plug this battery pack into the 30 pin connector. You can then either keep running with a fairly large dongle hanging off the bottom of your device, or wait and the battery pack will charge your device in 3.5 hours according to Monoprice (or about 2.5 hours according to my tests). It is just $14.50 and ugly for 1150 mAh.
This is especially impressive when compared to some of the more elegant competition, like the Morphie juice pack air with a capacity of 1200 mAh and a selling price of US$79 direct, or its larger sibling the Morphie juice pack holding 1800 mAh and selling for US$99 direct. But the Morphie is much nicer as a carrier.