I saw Scott's post on the Lenmar Power Pack and that reminded me that I had been wanting to post my portable power options. My first USB charger was a Duracell model I picked up at Meijer on the discountinued rack several years ago. It worked ok, but since them I've upgraded. :-)
First up is the Tekkeon MP1580 TEKCHARGE Mobile Power Pack and Battery Charger. I bought this one because it can take regular AA batteries. I also bought an 8 pack of the Sanyo Eneloop batteries. This way I can use the charger twice before I have to find an outlet. It's also pretty compact. Unfortunately, AA batteries aren't the best way to charge an iPhone, only bringing it up 30-40%.
Second is a Mophie Juice Pack for my iPhone. This one I almost always use anytime I know I'm not going to be near an outlet for an entire day. It will bring my phone up to about 60%. It's a little nicer than the USB chargers since I don't have to mess around with cables.
The final device I use is the Jackery Giant 10400mAh Premium Portable High Capacity Dual-Port External Battery Power Bank Backup Charger. This thing can charge my iPhone several times and I've read that it will charge my iPad 3 once (I haven't had a chance to try that out). It is heavy though, and bulkier than the above mentioned devices. I always carry it in my bag though, and if I am going out with friends I'll grab it and a couple of cables so I can charge their phones too (although I don't have an Apple device that require a Lightning cable, so I can't charge those).
p.s. For the Great Ohio Bike Adventure back in June I bought the AGPtek 5000mAh Solar Power Dual USB External Battery Pack and Charger. Although it does have two USB ports, one is for charging the battery. As a backup battery it worked fine, but the solar panel is basically on there for emergencies. After a full day of riding with it in the sun I could maybe get 5% charge onto my phone. That would be great if I was stuck somewhere and had to do a quick call or text, but I wouldn't buy it for it's solar panel.