I use the Energizer Energi To Go product. It optimally uses two AA Lithium Ultimates (E91), although reportedly AA alkalines will work. The model I purchased has mini and micro USB connectors.

Woot had them on sale about a month ago and I picked up six of them. To be clear, for me they are a emergency use item, not for regular phone charging. In this use, the lithiums are a good fit (cost/shelf life factors).