RAVPowerŽ 10000mAh USB battery pack w/ 5 charging tips - $29.99 + free shipping; dual USB wall charger - $5
Amazon has the RAVPower 10,000 mAh USB battery pack with 5 charging tips & carrying bag [amazon.com] for $39.99 - $10 coupon (JTVTWDNG) = $29.99. List price is $100.
I used one like this on a recent trip, and it saved us on more than one occasion. You don't realize quite how much you rely on your phone and other devices until you're in a strange place and they're all low on battery.
If you want an even better deal, add their dual-port USB travel wall charger [amazon.com] for only $5 more. $9.99 - $5 coupon (557COFR7) = $4.99. I believe this coupon is only valid when you purchase both items. The coupon for the battery is good with or without the charger.
Source: SlickDeal Popular Deal - RAVPowerŽ 10000mAh USB battery pack w/ 5 charging tips - $29.99 + free shipping; dual USB wall charger - $5
Amazon.com: RAVPowerŽ 10000mAh High Capacity Portable Power Bank / External Battery Pack Charger, Fit for iPad 4, iPad 3, iPad mini, iPhone 5; iPhone 4S; Samsung Galaxy S4, S3, S2, Galaxy Note 2; HTC Sensation, One X V One X V S, EVO 4G, Thunderbolt;